U.S. patent number 7,983,577 [Application Number 12/194,649] was granted by the patent office on 2011-07-19 for image forming apparatus.
This patent grant is currently assigned to Ricoh Company Limited. Invention is credited to Koichi Kato, Emi Kita, Maiko Koeda.
United States Patent |
7,983,577 |
Kita , et al. |
July 19, 2011 |
Image forming apparatus
Abstract
An image forming apparatus including an image bearing member; a
developing device forming a toner image; a toner supplying device
including a toner container, a toner feeding passage, a pump, in
which a first member is moved while rubbing a second member to feed
a developer supplement including at least the toner, and a residual
toner detector detecting the amount of the developer supplement
remaining in the toner container. Even after the toner container
achieves a near empty state, image forming operations are continued
as long as a predetermined condition is satisfied while changing
the pump's condition such that the pump is stopped, the ratio of
the pump stopping period to the pump driving period is set to be
greater than that before the near-empty detection, or the pump
stopping period and the pump driving period are set to be longer
than those before the near-empty detection.
Inventors: |
Kita; Emi (Tokyo,
JP), Kato; Koichi (Yokohama, JP), Koeda;
Maiko (Numazu, JP) |
Assignee: |
Ricoh Company Limited (Tokyo,
JP)
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Family
ID: |
40454584 |
Appl.
No.: |
12/194,649 |
Filed: |
August 20, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090074432 A1 |
Mar 19, 2009 |
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Foreign Application Priority Data
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Sep 14, 2007 [JP] |
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2007-239822 |
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Current U.S.
Class: |
399/27 |
Current CPC
Class: |
G03G
15/0877 (20130101); G03G 15/0856 (20130101); G03G
15/0893 (20130101) |
Current International
Class: |
G03G
15/08 (20060101) |
Field of
Search: |
;399/27,30 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2000-47465 |
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Feb 2000 |
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JP |
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2000-98721 |
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Apr 2000 |
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JP |
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Primary Examiner: Gray; David M
Assistant Examiner: Bonnette; Rodney
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. An image forming apparatus configured to perform image forming
operations to produce an image, comprising: an image bearing member
configured to bear an electrostatic image thereon; a developing
device, which has a developer containing portion containing a
developer including at least a toner and which is configured to
develop the electrostatic image with the developer to form a toner
image on the image bearing member; and a toner supplying device
configured to supply a developer supplement including at least the
toner to the developer containing portion, comprising: a toner
container containing the developer supplement; a feeding passage
configured to connect the toner container with the developer
containing portion; a pump, in which a first member is moved while
rubbing a second member to feed the developer supplement from the
toner container to the developer containing portion through the
feeding passage; and a residual toner detector configured to detect
an amount of the developer supplement remaining in the toner
container to determine whether the toner container is in a
near-empty state, wherein even after the residual toner detector
determines that the toner container is in a near-empty state, the
image forming apparatus continues the image forming operations as
long as a predetermined condition is satisfied while stopping the
pump.
2. The image forming apparatus according to claim 1, wherein the
pump is a screw pump including a rotor and a stator as the first
and second members, respectively, and wherein the stator is a
cylindrical elastic material having a spiral groove on an inner
surface thereof, and the rotor rotates while rubbing the inner
surface of the stator to feed the developer supplement toward an
axial direction of the rotor.
3. The image forming apparatus according to claim 1, wherein the
toner is prepared by a method including dissolving or dispersing
toner components including at least a polyester prepolymer
including a functional group having a nitrogen atom, a polyester, a
colorant, and a release agent in an organic solvent to prepare a
toner composition liquid, and subjecting the toner composition
liquid to a crosslinking reaction, a polymer chain growth reaction,
or a combination of a crosslinking reaction and a polymer chain
growth reaction in an aqueous medium.
4. The image forming apparatus according to claim 1, wherein the
developer in the developer containing portion of the developing
device includes a carrier and a toner, and the developer supplement
in the toner container includes the carrier and the toner, and
wherein a ratio (T/C) of the toner (T) to the carrier (C) in the
developer supplement is greater than that in the developer in the
developer containing portion.
5. An image forming apparatus configured to perform image forming
operations to produce an image, comprising: an image bearing member
configured to bear an electrostatic image thereon; a developing
device, which has a developer containing portion containing a
developer including at least a toner and which is configured to
develop the electrostatic image with the developer to form a toner
image on the image bearing member; and a toner supplying device
configured to supply a developer supplement including at least the
toner to the developer containing portion, comprising: a toner
container containing the developer supplement; a feeding passage
configured to connect the toner container with the developer
containing portion; a pump, in which a first member is moved while
rubbing a second member to feed the developer supplement from the
toner container to the developer containing portion through the
feeding passage; and a residual toner detector configured to detect
an amount of the developer supplement remaining in the toner
container to determine whether the toner container is in a
near-empty state, wherein even after the residual toner detector
determines that the toner container is in a near-empty state, the
image forming apparatus continues the image forming operations as
long as a predetermined condition is satisfied while changing a
condition of the pump such that a ratio (S/D) of a pump stopping
period (S) to a pump driving period (D) is greater than that before
the residual toner detector determines that the toner container is
in the near-empty state.
6. The image forming apparatus according to claim 5, wherein the
pump is a screw pump including a rotor and a stator as the first
and second members, respectively, and wherein the stator is a
cylindrical elastic material having a spiral groove on an inner
surface thereof, and the rotor rotates while rubbing the inner
surface of the stator to feed the developer supplement toward an
axial direction of the rotor.
7. The image forming apparatus according to claim 5, wherein the
toner is prepared by a method including dissolving or dispersing
toner components including at least a polyester prepolymer
including a functional group having a nitrogen atom, a polyester, a
colorant, and a release agent in an organic solvent to prepare a
toner composition liquid, and subjecting the toner composition
liquid to a crosslinking reaction, a polymer chain growth reaction,
or a combination of a crosslinking reaction and a polymer chain
growth reaction in an aqueous medium.
8. The image forming apparatus according to claim 5, wherein the
developer in the developer containing portion of the developing
device includes a carrier and a toner, and the developer supplement
in the toner container includes the carrier and the toner, and
wherein a ratio (T/C) of the toner (T) to the carrier (C) in the
developer supplement is greater than that in the developer in the
developer containing portion.
9. An image forming apparatus configured to perform image forming
operations to produce an image, comprising: an image bearing member
configured to bear an electrostatic image thereon; a developing
device, which has a developer containing portion containing a
developer including at least a toner and which is configured to
develop the electrostatic image with the developer to form a toner
image on the image bearing member; and a toner supplying device
configured to supply a developer supplement including at least the
toner to the developer containing portion, comprising: a toner
container containing the developer supplement; a feeding passage
configured to connect the toner container with the developer
containing portion; a pump, in which a first member is moved while
rubbing a second member to feed the developer supplement from the
toner container to the developer containing portion through the
feeding passage; and a residual toner detector configured to detect
an amount of the developer supplement remaining in the toner
container to determine whether the toner container is in a
near-empty state, wherein even after the residual toner detector
determines that the toner container is in a near-empty state, the
image forming apparatus continues the image forming operations as
long as a predetermined condition is satisfied while changing a
condition of the pump such that a pump stopping period (S) and a
pump driving period (D) are longer than those before the residual
toner detector determines that the toner container is in the
near-empty state.
10. The image forming apparatus according to claim 9, wherein the
pump is a screw pump including a rotor and a stator as the first
and second members, respectively, and wherein the stator is a
cylindrical elastic material having a spiral groove on an inner
surface thereof, and the rotor rotates while rubbing the inner
surface of the stator to feed the developer supplement toward an
axial direction of the rotor.
11. The image forming apparatus according to claim 9, wherein the
toner is prepared by a method including dissolving or dispersing
toner components including at least a polyester prepolymer
including a functional group having a nitrogen atom, a polyester, a
colorant, and a release agent in an organic solvent to prepare a
toner composition liquid, and subjecting the toner composition
liquid to a crosslinking reaction, a polymer chain growth reaction,
or a combination of a crosslinking reaction and a polymer chain
growth reaction in an aqueous medium.
12. The image forming apparatus according to claim 9, wherein the
developer in the developer containing portion of the developing
device includes a carrier and a toner, and the developer supplement
in the toner container includes the carrier and the toner, and
wherein a ratio (T/C) of the toner (T) to the carrier (C) in the
developer supplement is greater than that in the developer in the
developer containing portion.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus having
a toner supplying device for supplying a developer supplement (a
toner, a premix toner including a toner and a carrier or the like)
including at least a toner from a toner container to a developing
device.
2. Discussion of the Background
Image forming apparatus typically use a toner supplying device for
supplying a developer supplement (a toner, a premix toner including
a carrier and a toner or the like) including at least a toner from
a toner container to a developer containing portion of a developing
device of the apparatus. Japanese patent 3,917,761 (i.e., published
unexamined Japanese patent application No. 2000-47465) and
published unexamined Japanese patent application No. 2004-226524
(which corresponds to U.S. Pat. No. 7,123,865) have disclosed toner
supplying devices which supply a toner using a screw pump. Such
toner supplying devices include a toner feeding passage, and a
screw pump, which feeds the toner in the toner container to the
developer containing portion by suction through the toner feeding
passage.
Screw pumps typically include a stator which is made of an elastic
material and which has a spiral groove on the inner surface
thereof, and a rotor which is made of a metal and which has a
spiral form and rotates inside the stator. In such screw pumps, a
closed space is formed by the inner surface of the stator, the
surface of the rotor and the contact portion between the rotor and
the stator. When the rotor rotates, the rotor rubs the stator while
a contact portion of the rotor moves relative to the stator, and
therefore, the closed space moves in a direction parallel to the
axis of the rotor (i.e., the rotor axis direction). The screw pumps
have an opening at both the ends thereof in the rotor axis
direction, i.e., a first opening present on the uppermost stream
side relative to the moving direction of the closed space, and a
second opening present on the most downstream side. The first
opening serves as a suction opening (i.e., entrance), and the
second opening serves as an exhaust opening (i.e., an exit). The
first opening is connected with a toner container via a feeding
tube serving as a feeding passage. The second opening is connected
with a developer containing portion of a developing device directly
or via another feeding passage or a hopper.
When such a screw pump is set in a toner supplying device and then
driven, a negative pressure is generated at the suction opening due
to movement of the closed space caused by rotation of the rotor,
and thereby the toner in a toner container is sucked, resulting in
entering of the toner into the space between the stator and rotor
of the screw pump. The toner thus entering into the screw pump is
moved toward the exhaust opening due to movement of the closed
space while contained in the closed space. The toner thus fed to
the exhaust opening of the screw pump is supplied to a developer
containing portion of a developing device directly or via a feeding
passage or a hopper.
A toner supplying device having such a screw pump sucks and feeds a
toner using the screw pump. Therefore, even when the feeding tube
serving as a feeding passage is curved or raised at an acute angle,
the toner can be stably fed. Accordingly, by using a screw pump,
the positional flexibility of the toner supplying device and
developing device can be enhanced, namely the positions of the
toner supplying device and developing device can be changed
relatively freely. In addition, the feeding tube can be arranged
between parts set in the vicinity of the toner supplying device.
Therefore, the image forming apparatus can be miniaturized.
On the other hand, recently image forming apparatus are requested
to save energy. In order to save energy, fixing temperature in heat
fixing devices used for the image forming apparatus tends to be
decreased. Therefore, image forming apparatus using a low
temperature fixable toner, which can be fixed at a relatively low
fixing temperature, have been proposed.
Recent image forming apparatus typically have a function such that
when the toner in the toner container thereof is exhausted, a
message "toner is nearly empty" is displayed in the operation panel
of the image forming apparatus. Several methods have been used for
detecting that toner is nearly empty. One of the near-empty
detection methods is that a property (such as the amount of toner
present in a sub-hopper) influenced by the amount of toner fed by
the screw pump is measured at the main body of the image forming
apparatus to determine whether the toner in the toner container is
nearly empty. Specifically, this near-empty detection method is
such that when a sensor determines that the amount of toner present
in the sub-hopper is smaller than a predetermined amount, a
controller orders to perform a toner supplying operation. Even when
the amount of toner in the sub-hopper does not reach to the
predetermined amount even after a predetermined number of toner
supplying operations are performed, the controller determines that
the toner container is nearly empty.
There are image forming apparatus, which continue image forming
operations even after a near-empty detection as long as
predetermined conditions are satisfied (for example, conditions
such that the number of copies produced thereafter is within a
predetermined range, and/or the image forming time and/or the toner
consumption thereafter are within predetermined ranges are
satisfied). In this regard, the number of additional image forming
operations is determined as the number of images which can be
produced without any problems even when the toner is not supplied
from the toner container. It is common for conventional image
forming apparatus that even when a near-empty message is displayed,
a small amount of toner is present in the toner container.
Therefore, such image forming apparatus typically perform the toner
supplying operation in such additional image forming operations to
reduce the amount of the residual toner in the toner container.
However, when screw pumps feed a low temperature fixable toner, a
problem in that the suction power of the screw pumps deteriorate
tends to occur. The cause for the problem is considered as
follows.
When a rotor is rotated wile rubbing a stator in a screw pump, heat
is generated due to the friction between the rotor and the stator.
In addition, the rotor and stator form a closed space, and
therefore the thus generated heat does not easily escape from the
screw pump, resulting in increase of the internal temperature of
the screw pump. In this regard, when a considerable amount of toner
is present in the toner container, increase of the internal
temperature of the screw pump is prevented. This is because a
sufficient amount of toner is sucked by the screw pump, and the
toner in the screw pump absorbs the heat and is then discharged
from the screw pump, resulting in escape of the frictional heat
from the screw pump.
In contrast, when the toner present in the toner container is such
a small amount that a near-empty message is displayed, the amount
of toner sucked by the screw pump is little. The quantity of heat
discharged from the screw pump together with the toner decreases.
If the toner supplying operation is performed by the screw pump
similarly to the case where a sufficient amount of toner is present
in the toner container, the internal temperature of the screw pump
increases.
When the toner is a low temperature fixable toner, a problem in
that the toner is melted in the screw pump tends to occur. When the
toner is melted and then the internal temperature of the screw pump
decreases after the screw pump is stopped, the toner is fixed to
the stator and rotor. In this case, when the screw pump is driven
again, the stator (typically made of an elastic material) is easily
abraded by the toner, which is fixed to the contact portion between
the rotor and the stator and which serves as an abrasive. Thereby,
the sealing property of the screw pump is deteriorated due to the
abraded portion of the stator, resulting in deterioration of the
suction power of the screw pump.
This problem is not specific to such screw pumps, and may occur in
any pumps in which a first member is moved while rubbing a second
member contacted with the first member to generate a negative
pressure at the suction opening thereof.
Because of these reasons, a need exists for a toner supplying
method (or an image forming apparatus having a toner supplying
device), which does not cause the above-mentioned problem in that
the suction power of a pump (such as screw pumps) is deteriorated
due to fixation of a low temperature fixable toner to the pump.
SUMMARY OF THE INVENTION
As an aspect of the present invention, an image forming apparatus,
which performs image forming operations to produce an image, is
provided. The image forming apparatus includes:
an image bearing member configured to bear an electrostatic image
thereon;
a developing device, which has a developer containing portion
containing a developer including at least a toner and which is
configured to develop the electrostatic image with the developer to
form a toner image on the image bearing member; and
a toner supplying device configured to supply a developer
supplement including at least the toner (preferably, a premix toner
including a carrier and the toner when the developer is a
two-component developer) to the developer containing portion.
The toner supplying device includes:
a toner container containing the developer supplement;
a feeding passage configured to connect the toner container with
the developer containing portion;
a pump, in which a first member is moved while rubbing a second
member to feed the developer supplement from the toner container to
the developer containing portion through the feeding passage;
and
a residual toner detector configured to detect the amount of the
developer supplement remaining in the toner container to determine
whether the toner container is in a near-empty state.
Even after the residual toner detector detects that the toner
container is in a near-empty detection, the image forming apparatus
continues the image forming operations as long as a predetermined
condition is satisfied (for example, until a predetermined amount
of copies are produced, or the toner container is replaced with a
new toner container) while stopping the pump.
Instead of stopping the pump, the pump may perform control of drive
such that driving and stopping are repeatedly performed. In this
case, after the residual toner detector makes the near-empty
detection, the image forming apparatus continues the image forming
operations as long as the predetermined condition is satisfied
while changing the condition of the pump such that the ratio (S/D)
of the pump stopping period (S) to the pump driving period (D) is
greater than that before the residual toner detector makes the
near-empty detection or the pump stopping period (S) and the pump
driving period (D) are longer than the respective times (S) and
(D), respectively, before the residual toner detector makes the
near-empty detection.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other objects, features and attendant advantages of the
present invention will be more fully appreciated as the same
becomes better understood from the detailed description when
considered in connection with the accompanying drawings in which
like reference characters designate like corresponding parts
throughout and wherein:
FIG. 1 is a schematic cross-sectional view illustrating an example
(a copier) of the image forming apparatus of the present
invention;
FIG. 2 is a schematic cross-sectional view illustrating the
developing device and the image bearing member (photoreceptor) of
the image forming apparatus illustrated in FIG. 1;
FIG. 3 is a schematic view illustrating flow of the toner in the
developing device;
FIG. 4 is a schematic perspective view illustrating the developing
device of the image forming apparatus illustrated in FIG. 1;
FIG. 5 is a schematic perspective view illustrating the toner
supplying device of the image forming apparatus illustrated in FIG.
1;
FIG. 6 is a schematic cross-sectional view illustrating the toner
supplying device;
FIG. 7 is a schematic perspective view illustrating a toner
container (toner bottle) of the toner supplying device;
FIG. 8 is a schematic perspective view for explaining drive
transmission between a toner pump and a sub-hopper in the toner
supplying device;
FIG. 9 is a schematic perspective view illustrating the
sub-hopper;
FIG. 10 is a block diagram for explaining drive controlling of the
toner pump and the sub-hopper;
FIG. 11 is a timing chart for explaining drive controlling of a
screw pump in a background image forming apparatus;
FIG. 12 is a timing chart for explaining drive controlling of a
toner pump used for Example 1 of the image forming apparatus of the
present invention;
FIG. 13 is a timing chart for explaining drive controlling of a
toner pump used for Example 2 of the image forming apparatus of the
present invention;
FIG. 14 is a timing chart for explaining drive controlling of a
toner pump used for Example 3 of the image forming apparatus of the
present invention; and
FIG. 15 is a timing chart for explaining drive controlling of a
toner pump used for Example 4 of the image forming apparatus of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
At first, a tandem color laser copier, which is one example of the
image forming apparatus of the present invention and in which
plural photoreceptors are arranged in parallel, will be
explained.
FIG. 1 is a schematic view illustrating a tandem color laser copier
(hereinafter referred to as a copier). Referring to FIG. 1, a
copier 100 includes a printing section 150, a receiving material
feeding section 200 on which the printing section 150 is arranged,
a scanner 300 which is fixed on the printing section 150, and an
automatic document feeder (ADF) 400 which is fixed on the scanner
300.
The printing section 150 includes an image forming unit 20
including four process cartridges 18Y, 18M, 18C and 18K for forming
yellow (Y), magenta (M), cyan (C) and black (K) color images,
respectively. In this regards, a member with a suffix of Y, M, C or
K is a member used for forming a yellow, magenta, cyan or black
color image, respectively. The suffix is sometimes omitted if it is
not necessary for explanation. The printing section 150 further
includes an optical image writing unit 21, an intermediate transfer
unit 17, a secondary transfer device 22, a pair of registration
rollers 49, and a belt-type fixing device 25.
The optical image writing unit 21 includes a light source, a
polygon mirror, an f-.theta. lens, a reflection mirror, etc.,
(which are not shown in FIG. 1), and irradiates a photoreceptor
(explained later) with laser light on the basis of image data.
Each of the process cartridges 18(Y, M, C and K) includes a
photoreceptor 1, a charger, a developing device 4, a drum cleaning
device for cleaning the photoreceptor 1, a discharger for decaying
charges remaining on the photoreceptor 1, etc.
Hereinafter, the process cartridge 18Y for forming yellow color
images will be explained. At first, the circumferential surface of
the photoreceptor 1Y is charged with a charger (not shown). Next,
the optical image writing unit 21 irradiates the charged
photoreceptor 1Y with laser light, which has been modulated and
deflected, thereby decaying the charges of the irradiated portions
of the photoreceptor, resulting in formation of an electrostatic
latent image for a yellow image on the photoreceptor. Next, the
developing device 4Y develops the electrostatic latent image with a
developer including a yellow toner, resulting in formation of a
yellow toner image on the photoreceptor 1Y.
The thus prepared yellow toner image is then transferred onto an
intermediate transfer belt 110. This transfer process is
hereinafter referred to as primary image transfer. After the
primary image transfer, the surface of the photoreceptor 1Y is
cleaned with the drum cleaning device to remove residual toner
particles from the surface.
The thus cleaned photoreceptor 1Y is then discharged with the
discharger to remove residual charges therefrom. The
circumferential surface of the photoreceptor 1Y is then charged
with the charger so that the photoreceptor has an initial state,
i.e., the photoreceptor is ready for the next image forming
operations. The same image forming operations are performed on the
other photoreceptors 1M, 1C and 1K, resulting in formation of
magenta, cyan and black toner images on the respective
photoreceptors 1M, 1C and 1K.
Next, the intermediate transfer unit 17 will be explained.
The intermediate transfer unit 17 includes the intermediate
transfer belt 110, a belt cleaning device 90, a tension roller 14,
a driving roller 15 (which is driven with a belt driving motor (not
shown)), a secondary transfer backup roller 16, four primary
transfer bias rollers 62Y, 62M, 62C and 62K, etc.
The intermediate transfer belt 110 is supported while tightly
stretched by plural rollers including the tension roller 14, and is
clockwise rotated endlessly with the driving roller 15. The four
primary transfer bias rollers 62(Y, M, C and K) are arranged so as
to contact the inner surface of the intermediate transfer belt 110,
and receive a primary transfer bias from a power source (not
shown). The four primary transfer bias rollers 62 press the
intermediate transfer belt 110 toward the photoreceptors 1,
resulting in formation of four primary transfer nips. At the
primary transfer nips, primary transfer electric fields are formed
between the photoreceptors 1 and the primary transfer rollers 62
due to the primary transfer bias applied to the primary transfer
rollers.
The yellow toner image formed on the photoreceptor 1Y is primarily
transferred onto the intermediate transfer belt 110 due to the
primary transfer electric field and the nip pressure. Similarly,
the magenta, cyan and black toner images are sequentially
transferred onto the intermediate transfer belt to be overlaid on
the yellow toner image, resulting in formation of a combined four
color toner image on the intermediate transfer belt 110.
The combined four color toner image formed on the intermediate
transfer belt 110 is then transferred onto a paper sheet serving as
a receiving material (i.e., secondary image transfer) at a
secondary transfer nip (explained later). The surface of the
intermediate transfer belt 110 is cleaned with the belt cleaning
device 90 (which sandwiches the intermediate transfer belt 110 with
the driving roller 15) after the secondary image transfer to remove
residual toner particles therefrom.
Next, the secondary transfer device 22 will be explained.
The secondary transfer device 22 is located under the intermediate
transfer unit 17, and includes two tension rollers 23 and a feeding
belt 24, which is stretched by the tension rollers 23. The feeding
belt 24 is counterclockwise rotated while driven by at least one of
the tension rollers 23. The tension roller 23 on the right side in
FIG. 1 and the secondary transfer backup roller 16 sandwich the
intermediate transfer belt 110 and the feeding belt 24, resulting
in formation of a secondary transfer nip at which the intermediate
transfer belt 110 and the feeding belt 24 are contacted with each
other. A secondary transfer bias having a polarity opposite to that
of the charged toner is applied to the right tension roller 23 from
a power source (not shown), resulting in formation of a secondary
transfer electric field. Due to this secondary transfer electric
field, the combined color toner image on the intermediate transfer
belt 110 is electrostatically moved toward the feeding belt 24.
On the other hand, a paper sheet serving as a receiving material is
fed from the receiving material feeding section 200 to the pair of
registration rollers 49 as explained later in detail. The pair of
registration rollers 49 timely feed the paper sheet to the
secondary transfer nip. The combined color toner image on the
intermediate transfer belt 110 is transferred onto the paper sheet
at the secondary transfer nip due to the secondary transfer
electric field and the secondary transfer nip pressure. In this
regard, a transfer method in which the paper sheet may be charged
in a noncontact manner can be used instead of the above-mentioned
transfer method in which a secondary transfer bias is applied to
the right tension roller 23.
The receiving material feeding section 200 includes plural
cassettes 44, which are arranged in the vertical direction while
overlying with a space therebetween as illustrated in FIG. 1. In
each cassette 44, a feeding roller 42 is contacted with the
uppermost paper sheet (serving as a receiving material) in the
cassette. By rotating the feeding roller 42, the uppermost paper
sheet is fed toward a feeding passage 46.
The feeding passage 46 includes plural pairs of rollers 47 and the
pair of registration rollers 49, which are located at the end of
the feeding passage 46. The paper sheet is fed to the pair of
registration rollers 49 by the plural pairs of rollers 47 through a
passage 48. The paper sheet is then pinched by the pair of
registration rollers 49. On the other hand, the combined color
toner image fed toward the secondary transfer nip by the rotated
intermediate transfer belt 110. The pair of registration rollers 49
timely feed the paper sheet toward the secondary transfer nip so
that the combined color toner image is contacted with a proper
position of the paper sheet at the secondary transfer nip.
Therefore, the combined color toner image is transferred onto the
proper position of the paper sheet, resulting in formation of a
full color toner image on the paper sheet. The paper sheet bearing
the full color toner image thereon is then fed to the fixing device
25 by the feeding belt 24.
The fixing device 25 includes a belt unit in which a fixing belt 26
is rotated endlessly while stretched by two rollers, and a pressure
roller 27 pressed to one of the two rollers. The fixing belt 26 and
the pressure roller 27 are contacted with each other to form a
fixation nip. The paper sheet fed by the feeding belt 24 is pressed
at the fixation nip. The one of the two rollers, which is pressed
by the pressure roller 27, has a heat source therein to heat the
fixing belt 26. Therefore, the paper sheet is pressed and heated at
the fixation nip, resulting in fixation of the full color toner
image on the paper sheet.
The paper sheet bearing the fixed full color image thereon is
discharged from the main body of the image forming apparatus to a
tray 57 serving as a stacking member by a discharging roller 56.
Alternatively, when another image is formed on the backside of the
paper sheet, the paper sheet is fed toward the secondary transfer
nip by a reversing member 28. Numeral 105 denotes a switching pick
which reverses the paper sheet to the secondary transfer nip.
In order to prepare a copy of an original document, at first the
original document is set on a table 30 of the ADF 400. When the
original document is a page of a book-form document, the page of
the book-form original document is directly set on a glass table
32, which can be exposed by opening the ADF 400. After the
book-form original document is set on the glass table 32, the ADF
400 is closed to press the book-form original document toward the
glass table.
When a copy start switch is pressed after the original document is
set, an original document reading operation of the scanner 300 is
started. When the original document is set on the table 30 of the
ADF 400, the original document is fed to the glass table 32 and
then the original document reading operation is started. In the
original document reading operation, a first traveling member 33
and a second traveling member 34 start to travel, and light is
emitted from a light source, which is provided on the first
traveling member 33, toward the original document. Reflection light
reflected from the original document is reflected off a mirror
provided in the second traveling member 34, followed by entering
into a reading sensor 36 after passing through a focusing lens 35.
Thus, the reading sensor 36 obtains image information from the
incident light.
In parallel to the original document reading operation, the devices
in the process cartridges 18, the intermediate transfer unit 17,
the secondary transfer device 22, and the fixing device 25 are
driven to operate. The optical image writing unit 21 is also driven
to operate, and irradiates the charged photoreceptors 1 with
imagewise light (i.e., an optical image having the image
information obtained by the reading sensor 36), resulting in
formation of electrostatic latent images on the photoreceptors. As
mentioned above, the electrostatic latent images are developed with
the respective developers including the respective color toners,
resulting in formation of color toner images on the respective
photoreceptors 1.
In addition, at almost the same time when the original document
reading operation is started, a receiving material feeding
operation is started in the receiving material feeding section 200.
In the receiving material feeding operation, one of the feeding
rollers 42 is rotated to feed a paper sheet contained in one of the
cassettes 44 arranged in a receiving material bank 43. In this
regard, when plural paper sheets are fed, the paper sheets are
separated from each other by a separation roller 45. The paper
sheet is fed to the feeding passage 46, and is then fed to the
secondary transfer nip by the plural pairs of feeding rollers 47.
Alternatively, the receiving material feeding operation may be
performed using a manual feed tray 51. In this case, a feeding
roller 50 is rotated to feed paper sheets set on the manual feed
tray 51 one by one. The paper sheets are separated from each other
by a separation roller 52, and the paper sheet is fed to a manual
feeding passage 53.
When a multi-color image including two or more color images is
prepared, the upper portion of the intermediate transfer belt 110
is stretched by the rollers so as to be contacted with all the
photoreceptors 1Y, 1M, 1C and 1K. However, when a monochrome black
image is prepared, the upper portion of the intermediate transfer
belt 110 is declined so as to be separated from the photoreceptors
1Y, 1M, and 1C. In addition, among the four photoreceptors 1, only
the photoreceptor 1K for black images is counterclockwise rotated
so that a black toner image is formed on the photoreceptor 1K. In
this case, not only the photoreceptors 1Y, 1M and 1C, but also the
developing devices 4Y, 4M and 4C are stopped, to prevent wasteful
abrasion of the photoreceptors 1Y, 1M and 1C and wasteful
consumption of the Y, M and C developers.
The copier 100 includes a controller (not shown in FIG. 1)
including a CPU configured to control the operations of the various
devices included in the copier, and an operation panel (not shown)
including a display and keys. The operator can provide an
instruction to the controller by key input. For example, the
operator can select a one-side print mode among three one-side
print modes, i.e., direct discharge mode, reverse discharge mode
and decurling reverse discharge mode.
FIG. 2 is an enlarged view illustrating a portion of the process
cartridge 18, which portion includes the developing device 4 and
the photoreceptor 1. Since the process cartridges 18Y, 18M, 18C and
18K are the same except for the color of the toner used for
developing, the suffixes Y, M, C and K are omitted in FIG. 2.
As illustrated in FIG. 2, the photoreceptor 1 is rotated in a
direction indicated by an arrow G. The surface of the photoreceptor
is charged with a charger (not shown). The charged surface of the
photoreceptor 1 is exposed to imagewise light emitted from the
optical image writing unit 21, resulting in formation of an
electrostatic latent image on the photoreceptor 1. The
electrostatic latent image is developed with the toner in the
developer supplied from the developing device 4, resulting in
formation of a toner image on the photoreceptor 1.
The developing device 4 includes a developing roller 5, which
serves as a developer bearing member and which is rotated in a
direction indicated by an arrow I to supply the developer to the
electrostatic latent image on the photoreceptor 1, and a supplying
screw 8, which serves as a developer supplying member and which
supplies the developer to the developing roller 5 while feeding the
developer toward the inner portion thereof (i.e., in a direction of
from the front side of the paper sheet on which FIG. 2 is printed
to the backside of the paper sheet). The supplying screw 8 includes
a rotation shaft and a blade provided on the rotation shaft, and
serves as a developer feeding screw, which feeds the developer in
the axis direction thereof by rotating.
A doctor blade 12 is provided on a downstream side from the opposed
position, at which the developing roller 5 and the supplying screw
8 are opposed, relative to the rotation direction I of the
developing roller. The doctor blade 12 serves as a developer layer
thickness controlling member configured to control the thickness of
the developer layer on the developing roller 5.
The developing device 4 further includes a collection screw 6,
which is provided on a downstream side from the opposed position,
at which the developing roller 5 and the photoreceptor 1 are
opposed, relative to the rotation direction I of the developing
roller. The collection screw 6 collects the developer used for
developing and feeds the collected developer toward the inner
portion of the collection screw 6 (i.e., in the same direction as
that of the feeding direction of the supplying screw 8). As
illustrated in FIG. 2, a developer supplying passage 9 is provided
on one side of the supplying screw 8, and a developer collection
passage 7 is provided on an upper side of the collection screw
6.
The developing device 4 further includes a developer agitating
passage 10, which is located below the developer supplying passage
9 and is parallel to the developer collection passage 7. The
developer agitating passage 10 includes an agitation screw 11
configured to feed the developer in the direction opposite to the
developer feeding direction of the supplying screw 8 while
agitating the developer. The developer agitating passage 10 is
separated from the developer supplying passage 9 with a portion of
a first partition wall 133. An opening is formed on both ends of
the first partition wall 133 in the developer feeding direction of
the supplying screw 8, and therefore the developer supplying
passage 9 and the developer agitating passage 10 are communicated
with each other through the openings.
The developer supplying passage 9 is separated from developer
collection passage 7 with another portion of the first partition
wall 133, which portion includes no opening.
The developer agitating passage 10 is separated from the developer
collection passage 7 with a second partition wall 134. The second
partition wall 134 has one opening on an uppermost stream side in
the developer feeding direction of the supplying screw 8, and
thereby the developer agitating passage 10 is communicated with the
developer collection passage 7. The developer containing portion of
the developing device 4 is constituted of the developer supplying
passage 9, the developer collection passage 7 and the developer
agitating passage 10.
The developer used for developing electrostatic latent images is
collected with the developer collection passage 7 and the collected
developer is fed in the direction opposite to the developer feeding
direction of the supplying screw 8. The thus fed developer is then
fed to the agitating passage 10 through one of the openings of the
first partition wall 133, which is located on a portion
corresponding to a non-image-forming area of the photoreceptor 1
and which is located on the downstream side relative to the
developer feeding direction of the developer collection passage 7.
At a portion of the developer agitating passage 10, which is
located on an upstream side relative to the developer feeding
direction of the developer agitating passage 10 and which faces one
of the openings of the first partition wall 133, a premixed toner
including a carrier and a toner is supplied to the developer
agitating passage 10 from a toner supplying opening provided above
the developer agitating passage 10.
Next, flow of the developer in the three developer passages 9, 7
and 10 will be explained.
FIG. 3 is a schematic view for explaining flow of the developer in
the three developer passages. In FIG. 3, arrows indicate the moving
directions of the developer.
The developer is supplied from the developer agitating passage 10
to the developer supplying passage 9 through an opening 91 as
indicated by an arrow D. The developer supplying passage 9 supplies
the developer to the developing roller 5 while feeding the
developer in the developer feeding direction of the supplying screw
8 as indicated by three outline arrows. The developer (i.e.,
excessive developer), which is supplied to the developing roller 5
but is not used for developing until the developer is fed to the
downstream side of the supplying passage 9, is returned to the
developer agitating passage 10 through another opening 92 as
indicated by an arrow E.
On the other hand, the developer fed to the developer collection
passage 7 from the developing roller 5 is fed by the collection
screw 6. The developer (collected developer) fed to the downstream
side of the developer collection passage 7 is fed to the developer
agitating passage 10 through a collection-use opening 93 as
indicated by an arrow F.
In the developer agitating passage 10, the excessive developer and
the collected developer are agitated, and the mixture is fed to the
downstream side of the developer agitating passage 10 (i.e., the
upstream side of the developer supplying passage 9) with the
agitating screw 11. The thus fed mixture developer is fed to the
developer supplying passage 9 through the opening 91 of the first
partition wall 133 as indicated by the arrow D.
In addition, a premix toner, which includes the carrier and the
toner and which serves as the developer supplement, is supplied to
the developer agitating passage 10, if necessary. The premix toner
is mixed with the collected developer, and the excess developer,
and the mixture developer is fed to the downstream side of the
developer agitating passage 10 (i.e., the upstream side of the
developer supplying passage 9) with the agitating screw 11 as
mentioned above. A toner concentration sensor (not shown) is
provided on a lower portion of the developer agitating passage 10.
Depending on the output of the toner concentration sensor, the
developing device 4 performs a toner supplying operation (mentioned
later) in which the developer supplement (i.e., toner or premix
toner) is supplied from the toner container.
The developing device 4 illustrated in FIG. 3 includes the
developer supplying passage 9 and the developer collection passage
7 so that developer supplying and developer collection are
performed in the different passages. Therefore, it is impossible
that the developer, which has been used for developing, is mixed
with the developer in the developer supplying passage 9. Therefore,
occurrence of a problem in that the developer located on the
downstream side of the developer supplying passage 9 has a lower
toner concentration than the developer in the other portions of the
developer supplying passage 9 can be prevented.
In addition, the developing device 4 includes the developer
collection passage 7 and the developer agitating passage 10 so that
developer collection and developer agitation are performed in the
different passages. Therefore, the developer, which has been used
for developing, never falls into the developer in process of
agitating. Thus, the well agitated developer is supplied to the
developer supplying passage 9. Therefore, the developer in the
developer supplying passage 9 has a constant toner concentration
and charge in the developer feeding direction, thereby forming
toner images having a constant image density on the photoreceptors
1.
Next, the way to supply the developer supplement (i.e., toner or
premix toner) to the three developer passages 9, 10 and 7 will be
explained referring to FIG. 4, which is a schematic perspective
view illustrating the developing device 4. Hereinafter, an example,
in which a premix toner including a carrier and a toner is supplied
as the developer supplement from a toner container to the
developing device, will be explained. However, the present
invention is not limited thereto, and a toner may be supplied as
the developer supplement instead of a premix toner.
As illustrated in FIG. 4, a toner supplying opening 95 configured
to supply a premix toner is provided over an upstream portion of
the developer agitating passage 10 having the agitating screw 11
relative to the developer feeding direction in the developer
agitating passage 10. The toner supplying opening 95 is located
outside of the side end of the developing roller 5. The location of
the toner supplying opening 95 is not limited to the
above-mentioned location, and may be formed over a downstream
portion of the developer collection passage 7 relative to the
developer feeding direction in the developer collection passage
7.
In addition, the toner supplying opening 95 may be formed over the
collection-use opening 93 (illustrated in FIG. 3) through which the
developer is transferred. In this case, the premix toner can be
efficiently mixed with the developer because the developer is well
mixed at the collection-use opening 93.
Next, a toner supplying device, which serves as a developer
supplying device configured to supply the premix toner to the
developing device through the toner supplying opening 95, will be
explained by reference to FIGS. 5-9.
FIG. 5 is a schematic perspective view illustrating a toner
supplying device 500 of the copier 100. FIG. 6 is a cross-sectional
view illustrating the toner supplying device 500. FIG. 7 is a
schematic perspective view illustrating a toner bottle 120 serving
as a developer container (or powder container). FIG. 8 is a
schematic view illustrating a drive transmission portion of the
toner supplying device 500 at which driving force is transmitted
between a toner pump 60 and a sub-hopper 68. FIG. 9 is a schematic
perspective view illustrating the sub-hopper.
The toner bottle 120 contains a premix toner, which is a mixture of
a carrier and a toner, as the developer supplement, wherein the
concentration of the toner in the premix toner is higher than that
in the developer in the developing device 4. In FIG. 5, a character
Tf denotes flow of the premix toner.
The copier 100, which is a tandem image forming apparatus, has a
configuration such that plural toner bottles 120 containing
respective premix color toners are arranged side by side as
illustrated in FIG. 5. The toner bottles 120 are connected with
respective supplying units each including the sub-hopper 68 and the
toner pump 60 through respective toner supplying tubes 65. The
developing devices 4 are connected with lower portions of the
respective supplying units.
In this example, the toner pump 60 serving as a pumping device is a
mohno pump which is a screw pump and which includes a stator 69 and
a rotor 61 (illustrated in FIG. 6) configured to feed the premix
toner in the axis direction thereof by rotating in the stator. The
stator 69 is made of an elastic material and has a spiral groove on
the inner surface thereof. For example, pumps described in JP-A
2000-98721 can be used for the toner pump 60.
As illustrated in FIGS. 6 and 7, the toner bottle 120 includes a
toner containing portion 121 serving as a powder containing
portion, a toner discharging opening 122 and a cap 130 attached to
the toner discharging opening 122. The toner bottle 120 will be
explained later in detail.
When the toner bottle 120 is set to the main body of the copier
100, the tip of a nozzle 80 serving as a connecting member is
inserted into the cap 130, and thereby the toner discharging
opening 122 is engaged with a toner receiving opening of the nozzle
80. The nozzle 80 has a joint connected with the toner supplying
tube 65, the other end of which is connected with the toner pump
60. In addition, the toner pump 60 is connected with the developing
device 4 through the sub-hopper 68. Thus, when the toner bottle 120
is set to the main body of the copier 100, the toner bottle 120 is
connected with the developing device 4. Referring to FIG. 6,
numeral 125 denotes a cylindrical shutter. In FIG. 6, the shutter
125 is pushed out by a nozzle provided on the main body of the
image forming apparatus so that the premix toner in the toner
bottle 120 is discharged.
The toner pump 60 is a suction-type uniaxial eccentric screw pump,
and includes the rotor 61 and the stator 69 as mentioned above. The
rotor 61 is a spirally-twisted shaft having a circle cross section,
and is connected with a driving motor 66 via the drive transmission
portion and a universal joint 64 as illustrated in FIG. 6. The
stator 69 is made of an elastic material such as rubbers and has a
twisted hole having an oval cross section. The pitch of the spiral
groove formed on the inner surface of the stator 69 is twice the
pitch of the spirally-twisted rotor 61 as illustrated in FIG. 6. By
rotating the rotor 61 in the stator 69, the premix toner in the
space formed between the rotor and the stator can be fed.
Namely, by rotating the rotor 61 without rotating the stator 69,
the rotor is moved while rubbing the stator, resulting in formation
of a negative pressure at a toner suction opening 63, thereby
forming airflow in the toner supplying tube 65.
Thus, when the toner pump 60 is operated and the rotor 61 is
rotated, the premix toner in the toner bottle 120 is fed to the
toner pump 60 through the toner suction opening 63. The thus fed
premix toner is then fed from the left side to the right side (in
FIG. 6) by suction. The premix toner is then supplied to the
developing device 4 through the toner supplying opening 95 via a
toner discharging opening 67 and the sub-hopper 68.
In FIG. 6, drive transmission of from the driving motor 66 to the
universal joint 64 is schematically illustrated. The drive
transmission portion for transmitting the driving force of the
driving motor 66 to the universal joint 64 will be explained in
detail by reference to FIG. 8.
When the driving motor 66 illustrated in FIG. 8 rotates, a driving
shaft 66b is rotated, and first and second shaft gears 66a and 66c,
which are connected with the driving shaft 66b, are also rotated.
When the first shaft gear 66a is rotated, the driving force is
transmitted to a pump drive clutch 60a. A controller 600
(illustrated in FIG. 10), which is a control board present in the
main body of the copier, performs controlling such that when the
pump driving clutch 60a is turned on, the driving force is
transmitted to a shaft drive gear 64a via a pump idler gear 64b,
thereby rotating the rotor 61.
On the other hand, when the second shaft gear 66c is rotated,
driving force is transmitted to a sub-hopper drive clutch 68a. The
controller 600 performs controlling such that when the sub-hopper
drive clutch 68a is turned on, the driving force is transmitted to
the sub-hopper 68 via an idler gear train 68b, thereby rotating
screws of the sub-hopper (which are explained later).
Next, the sub-hopper 68 will be explained by reference to FIG.
9.
The sub-hopper 68 includes an upper casing 608 and a lower casing
609. The space formed by the upper and lower casings 608 and 609 is
separated with a partition plate 604. A first upper screw 601 and a
second upper screw 602 are located in the upper casing 608. In
addition, an upper partition wall 603 having openings at both ends
thereof is provided between the first and second upper screws 601
and 602.
A lower screw 606 is located in the lower casing 609, and the
partition plate 604 has an opening 605 configured to connect the
upper space of the sub-hopper 68 with the lower space of the
sub-hopper 68.
Flow of the premix toner is shown by curved arrows in FIG. 9. The
premix toner from the toner pump 60 is supplied to the sub-hopper
68 as illustrated by an arrow .alpha.. In addition, the premix
toner is supplied from the sub-hopper 68 to the developing device 4
as illustrated by an arrow .beta..
When the driving force is input to the sub-hopper 68 via the idler
gear train 68b, the first and second upper screws 601 and 602, and
the lower screw 606 are rotated. In this case, the first and second
upper screws 601 and 602 feed the premix toner in different
directions, and therefore the premix toner is circulated in the
upper casing 601 while agitated.
A joint opening 611 located on a lower portion of the sub-hopper
case is connected with the toner supplying opening 95 (illustrated
in FIG. 4) formed on the screw case located on the front end
portion of the developing device 4. When the screws in the
sub-hopper 68 are rotated, the premix toner is supplied from the
sub-hopper to the developing device 4 through the joint opening
611.
A part of the premix toner agitated by the first and second upper
screws 601 and 602 is supplied to one end of the lower casing 609
through the opening 605. The premix toner supplied to the lower
casing 609 is fed to the joint opening 611 by rotation of the lower
screw 606. Thus, the premix toner is supplied to the developing
device 4.
In this regard, a vibration-type toner sensor 610 is provided in
the vicinity of the first upper screw 601 in the upper casing 608
to determine whether the predetermined amount of premix toner is
present in the sub-hopper 68 with the detection surface of the
sensor, which is contacted with the premix toner in the upper
casing 608.
FIG. 7 is a perspective view illustrating the toner bottle 120.
Referring to FIG. 7, the toner containing portion 121 of the toner
bottle 120 containing a premix toner Tp is a bag (i.e., a soft
package) prepared by welding a sheet of resin or the like. The
sheet is typically prepared by laminating plural different resin
films. Specifically, the sheet is typically formed of an inner
layer made of a weldable material, an intermediate layer made of an
airtight material, and an outer layer made of a rigid material.
Specific examples of the weldable materials for use in the inner
layer include polyethylene resins and the like, which can be melted
at a relatively low temperature. Specific examples of the airtight
materials and rigid materials include polyethylene terephthalate
resins (PET), nylon resins, aluminum sheets, paper sheets, etc. The
materials used for these layers are determined depending on the
material (i.e., solid, liquid, powder, etc.) to be contained
therein, and the purpose of the bag (i.e., food-use, medical-use,
etc.). In this example, the toner containing portion 121 is made of
a polyethylene film serving as the inner layer, a nylon film
serving as the intermediate layer, and a PET film serving as the
outer layer.
The layers of the toner containing portion 121 will be explained in
detail.
By using a material, which can be easily melted at a relatively low
temperature, for the inner layer of the toner containing portion
121, the layer is evenly melted upon application of heat thereto
and thereby both the ends of the sheet can be adhered with each
other without a space therebetween
The intermediate layer prevents the premix toner Tp from being
exposed to ambient air when the toner bottle 120 is stored. When
the premix toner is exposed to air, the premix toner is often
deteriorated. For example, the premix toner often agglomerates
particularly under high humidity conditions. In this case, the
premix toner cannot be easily supplied to the developing device. In
order to prevent occurrence of such a problem, the toner bottle has
the intermediate layer formed of an airtight material.
In addition, the users directly contact the toner bottle, and
therefore the toner bottle preferably has a good handling property.
By using a rigid material for the outer layer while adjusting the
thickness of the layer, a proper rigidity can be imparted to the
toner bottle.
The sheet constituting the toner bottle can include one or more
layers in addition to these three layers.
The toner containing portion 121 is prepared by folding a sheet in
such a manner that the end portions of the inner layer are
contacted with each other, and then the contacted end portions are
heated. By performing this operation plural times on other end
portions of the sheet, a bag for use as the toner containing
portion 121 can be prepared.
The method for preparing the toner containing portion 121 is not
limited thereto, and a method in which the end portions of the
sheet are adhered to each other with an adhesive can also be used.
For example, paper bags can be preferably prepared by this method.
Since the ridge lines of a bag prepared by this method are formed
by folding the sheet, the ridge lines have the same strength as
that of the other portions of the bag.
In contrast, the bag prepared by the above-mentioned welding method
has a welded portion 123 at the ridge lines thereof as illustrated
in FIG. 7. Since the welded portion 123 includes two sheets, the
thickness thereof is about twice the thickness of the other portion
of the bag. Therefore, since the welded portion 123 serves as a
pillar, the bag has a good rigidity. Such a rigid bag can prevent
occurrence of problems in that the toner container is buckled or
the portion of the toner bottle in the vicinity of the toner
discharging opening 122 is deformed due to vibration in
transportation and impact in handling, resulting in clogging of the
toner bottle with the premix toner.
As mentioned above, the toner containing portion 121 is made of a
sheet, and therefore the toner containing portion can be deformed.
Therefore, even when the amount of the premix toner is changed or
the properties (such as shapes) of the premix toner are changed,
the toner containing portion can change its shape so as to fit the
premix toner therein. In addition, after use the toner bottle can
be collected by being rounded or folded. Thus, the toner bottle has
good handling property.
Since it is difficult to fix the deformable toner containing
portion 121 to the toner supplying device 500, the toner containing
portion 121 is set to the cap 130 made of a hard resin, etc. Since
the cap is engageable with the toner supplying device 500, the
toner bottle can be securely set to the toner supplying device 500.
The cap 130 is made of a molded resin having high rigidity. By
preparing the inner layer of the toner containing portion 121 and
the cap 130 using polyethylene, the cap can be easily attached to
the toner containing portion 121 without a space therebetween by a
welding method. Specifically, at first a part of the cap 130 is
inserted into the toner containing portion 121, and then the
connected portion is heated with a welding device. By using this
method, the cap 130 can be securely fixed to the toner containing
portion 121.
The cap 130 has an attaching part 136 to be engaged with the main
body of the copier 100. The forms of the attaching parts 136 of the
toner bottles 120 for yellow, magenta, cyan and black toners are
different from each other. Therefore, occurrence of a problem in
that a toner bottle 120 is set to a wrong position can be
prevented. In addition, a RF tag 124 is attached to one side of the
cap 130. The RF tag 124 is an information recording medium in which
data stored in the memory thereof are read or rewritten in a
noncontact manner using an electric wave (electromagnetic wave).
The RF tag stores information such as names of the image forming
apparatus for which the premix toner contained in the toner bottle
can be used, color of the premix toner, manufacturing date of the
premix toner, and amount of residual premix toner in the toner
bottle.
Next, the way to replace the developer in the developing device 4
will be explained by reference to FIGS. 2 and 3.
The toner supplying device 500 supplies the premix toner, which
includes a carrier and a toner and which is contained in the toner
bottle 120, to the developing device 4 through the toner supplying
opening 95.
The developing device 4 includes a developer discharging opening 94
from which a part of the developer is discharged when the volume of
the developer in the developer supplying passage 9 exceeds a
predetermined volume, and a developer discharge passage 2
configured to discharge the excess developer from the developing
device 4. As illustrated in FIG. 3, the developer discharge passage
2 is located on the downstream side of the developer supplying
passage 9 relative to the developer feeding direction while
separated from the developer supplying passage 9 with a partition
135. The developer discharging opening 94 is formed on the
partition 135 so that the developer supplying passage 94 is engaged
with the developer discharging passage 2.
In the developing device 4, the developer stays in the vicinity of
the downstream side of the developer supplying passage 9 (this
portion is hereinafter sometimes referred to as a developer staying
position) depending on the amount of the developer fed through the
developer supplying passage 9, the amount of the developer (excess
developer) supplied to the developing roller 5, and the amount of
the developer moving from the developer supplying passage 9 to the
developer agitating passage 10 through the opening 92. When the
amount of the developer in the developing device 4 is constant, the
amount (per unit time) of the developer fed to the downstream side
of the developer supplying passage 9 is almost equal to the amount
(per unit time) of the developer moving from the developer
supplying passage 9 to the developer agitating passage 10 through
the opening 92. Therefore, the volume of the developer staying in
the vicinity of the downstream side of the developer supplying
passage 9 is constant in this case.
However, when the amount of the developer in the developing device
4 increases, the amount of the developer fed to the downstream side
of the developer supplying passage 9 becomes greater than the
amount of the developer moving from the developer supplying passage
9 to the developer agitating passage 10 through the opening 92.
Therefore, the volume of the developer present at the developer
staying position increases.
The developer discharging opening 94 is arranged at the developer
staying position. When the developer staying at the developer
staying position increases and exceeds the upper end of the
developer discharging opening 94, the excess developer is
discharged from the developer supplying passage 9 to the developer
discharging passage 2.
When the premix toner is not supplied from the toner supplying
device 500 to the developing device 4, the amount of the developer
in the developing device hardly changes, and therefore the amount
of the developer staying at the developer staying position hardly
changes. In contrast, when the premix toner is supplied from the
toner supplying device 500 to the developing device 4, the amount
of the developer in the developing device increases, and therefore
the amount of the developer staying at the developer staying
position increases. In this case, when the developer staying at the
developer staying position reaches the developer discharging
opening 94, the excess developer is discharged from the developer
supplying passage 9 to the developer discharging passage 2 through
the opening 94. The excess developer is then discharged from the
developing device. Referring to FIG. 2, numeral 2a denotes a
discharging screw for discharging the excess developer from the
developing device, which is provided in the discharging passage
2.
In this regard, the developer discharged from the developing device
4 includes the carrier and the toner while the premix toner
supplied to the developer includes a fresh developer and a fresh
toner. Therefore, partial replacement of the developer in the
developing device is performed.
In conventional image forming apparatus having a developing device
using a two-component developer including a carrier and a toner, it
is typical to supply only the toner to the developing device in an
amount equal to the amount of the toner used for developing images.
Such image forming apparatus have a drawback in that the developer
in the developing device deteriorates after repeated use, resulting
in occurrence of problems in that the image qualities deteriorate
and the toner scatters around the developing device. Therefore, it
is necessary for a service person to frequently perform a
maintenance operation in which the developer in the developing
device is replaced with a fresh developer.
In contrast, a premix toner including a carrier and a toner is
supplied to the developing device 4 in the copier 100 of the
present invention, and therefore the developer can be replaced with
a fresh developer while image forming operations are performed.
Therefore, the life of the developer is prolonged, and thereby the
interval between maintenance operations is extended, resulting in
decrease of the down time of the image forming apparatus.
The toner used for the premix toner contained in the toner bottle
120 is preferably a toner prepared by a method including dissolving
or dispersing toner components including at least a polyester
prepolymer having a group including a nitrogen atom, a polyester, a
colorant and a release agent in an organic solvent to prepare a
toner composition liquid, and subjecting the toner composition
liquid to a crosslinking reaction and/or a polymer chain growth
reaction in an aqueous medium. This toner has good low temperature
fixability. By using such a toner, the fixing temperature of the
fixing device 25 can be decreased, resulting in decrease of the
energy consumption of the fixing device 25 and the copier 100.
Next, the toner components and the toner preparation method will be
explained.
(Polyester)
Polyesters for use in the toner for use in the image forming
apparatus of the present invention is prepared by subjecting a
polyol with a polycarboxylic acid to a polycondensation
reaction.
Suitable polyols (PO) for use in preparing the polyesters include
diols (DIO), polyols (TO) having three or more hydroxyl groups, and
mixtures of DIO and TO. Preferably, diols (DIO) alone or mixtures
of a diol (DIO) and a small amount of polyol (TO) are used.
Specific examples of the diols (DIO) include alkylene glycols,
alkylene ether glycols, alicyclic diols, bisphenols, alkylene oxide
adducts of alicyclic diols, alkylene oxide adducts of bisphenols,
etc.
Specific examples of the alkylene glycols include ethylene glycol,
1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol and
1,6-hexanediol. Specific examples of the alkylene ether glycols
include diethylene glycol, triethylene glycol, dipropylene glycol,
polyethylene glycol, polypropylene glycol and polytetramethylene
ether glycol. Specific examples of the alicyclic diols include
1,4-cyclohexane dimethanol and hydrogenated bisphenol A. Specific
examples of the bisphenols include bisphenol A, bisphenol F and
bisphenol S. Specific examples of the alkylene oxide adducts of
alicyclic diols include adducts of the alicyclic diols mentioned
above with an alkylene oxide (e.g., ethylene oxide, propylene oxide
and butylene oxide). Specific examples of the alkylene oxide
adducts of bisphenols include adducts of the bisphenols mentioned
above with an alkylene oxide (e.g., ethylene oxide, propylene oxide
and butylene oxide).
Among these compounds, alkylene glycols having from 2 to 12 carbon
atoms and alkylene oxide adducts of bisphenols are preferable. More
preferably, alkylene oxide adducts of bisphenols, and mixtures of
an alkylene oxide adduct of a bisphenol and an alkylene glycol
having from 2 to 12 carbon atoms are used.
Specific examples of the polyols (TO) include aliphatic alcohols
having three or more hydroxyl groups (e.g., glycerin, trimethylol
ethane, trimethylol propane, pentaerythritol and sorbitol);
polyphenols having three or more hydroxyl groups (trisphenol PA,
phenol novolak and cresol novolak); adducts of the polyphenols
mentioned above with an alkylene oxide such as ethylene oxide,
propylene oxide and butylene oxide; etc.
Suitable polycarboxylic acids (PC) for use in preparing the
polyesters include dicarboxylic acids (DIC) and polycarboxylic
acids (TC) having three or more carboxyl groups. Preferably,
dicarboxylic acids (DIC) alone and mixtures of a dicarboxylic acid
(DIC) with a small amount of polycarboxylic acid (TC) are used.
Specific examples of the dicarboxylic acids (DIC) include alkylene
dicarboxylic acids (e.g., succinic acid, adipic acid and sebacic
acid); alkenylene dicarboxylic acids (e.g., maleic acid and fumaric
acid); aromatic dicarboxylic acids (e.g., phthalic acid,
isophthalic acid, terephthalic acid and naphthalene dicarboxylic
acids; etc. Among these compounds, alkenylene dicarboxylic acids
having from 4 to 20 carbon atoms and aromatic dicarboxylic acids
having from 8 to 20 carbon atoms are preferably used.
Specific examples of the polycarboxylic acids (TC) having three or
more hydroxyl groups include aromatic polycarboxylic acids having
from 9 to 20 carbon atoms (e.g., trimellitic acid and pyromellitic
acid).
When a polycarboxylic acid (PC) is reacted with a polyol (PO),
anhydrides or lower alkyl esters (e.g., methyl esters, ethyl esters
or isopropyl esters) of the polycarboxylic acids mentioned above
can also be used as the polycarboxylic acid (PC).
Suitable mixing ratio (i.e., the equivalence ratio [OH]/[COOH]) of
the [OH] group of a polyol (PO) to the [COOH] group of a
polycarboxylic acid (PC) is from 2/1 to 1/1, preferably from 1.5/1
to 1/1 and more preferably from 1.3/1 to 1.02/1.
The polycondensation reaction of a polol with a polycarboxylic acid
is performed by heating the compounds to a temperature of from 150
to 280.degree. C. in the presence of an esterification catalyst
such as tetrabutoxytitanate and dibutyl tin oxide while removing
generated water (under a reduced pressure if necessary) to prepare
a polyester having a hydroxyl group. The hydroxyl value of the
polyester is preferably not less than 5 mgKOH/g, and the acid value
thereof is preferably from 1 to 30 mgKOH/g, and more preferably
from 5 to 20 mgKOH/g. When a polyester having a proper acid value
is used, a negative charging property can be imparted to the
resultant toner. In addition, the adhesion of the toner to
receiving papers can be improved, resulting in improvement of low
temperature fixability of the toner. However, when the acid value
is too high, the charging stability of the toner deteriorates
(particularly the charging property of the toner varies when
environmental conditions (such as humidity) change).
The weight average molecular weight of the polyester to be included
in the toner for use in the present invention is preferably from
10,000 to 400,000, and more preferably from 20,000 to 200,000. When
the weight average molecular weight is too low, the offset
resistance of the toner deteriorates. In contrast, when the weight
average molecular weight is too high, the low temperature
fixability of the toner deteriorates.
The polyesters prepared by the above-mentioned polycondensation
reaction are unmodified polyesters. In addition to the unmodified
polyesters, urea-modified polyesters can be used for the toner.
Such a urea-modified polyester is prepared by reacting a carboxyl
group or a hydroxyl group present at the end portions of the
unmodified polyester with a polyisocyanate compound (PIC) to
prepare a polyester prepolymer having an isocyanate group, and then
reacting the polyester prepolymer with an amine to perform a
crosslinking reaction and/or a polymer chain growth reaction.
Specific examples of the polyisocyanates (PIC) for use in preparing
the modified polyester resin include aliphatic polyisocyanates
(e.g., tetramethylene diisocyanate, hexamethylene diisocyanate and
2,6-diisocyanate methylcaproate); alicyclic polyisocyanates (e.g.,
isophorone diisocyanate and cyclohexylmethane diisocyanate);
aromatic diisocianates (e.g., tolylene diisocyanate and
diphenylmethane diisocyanate); aromatic aliphatic diisocyanates
(e.g., .alpha., .alpha., .alpha.', .alpha.'-tetramethyl xylylene
diisocyanate); isocyanurates; blocked polyisocyanates in which the
polyisocyanates mentioned above are blocked with phenol
derivatives, oximes or caprolactams; etc. These compounds can be
used alone or in combination.
Suitable mixing ratio (i.e., the equivalence ratio [NCO]/[OH]) of
the [NCO] group of a polyisocyanate (PIC) to the [OH] group of a
polyester is from 5/1 to 1/1, preferably from 4/1 to 1.2/1 and more
preferably from 2.5/1 to 1.5/1. When the [NCO]/[OH] ratio is too
large, the low temperature fixability of the toner deteriorates. In
contrast, when the ratio is too small, the content of the urea
group in the urea-modified polyesters decreases, thereby
deteriorating the hot-offset resistance of the toner.
The content of the polyisocyanate unit in the polyester prepolymer
(A) having an isocyanate group is from 0.5 to 40% by weight,
preferably from 1 to 30% by weight and more preferably from 2 to
20% by weight. When the content is too low, the hot offset
resistance of the toner deteriorates and in addition a good
combination of preservability and low temperature fixability cannot
be imparted to the resultant toner. In contrast, when the content
is too high, the low temperature fixability of the toner
deteriorates.
The average number of the isocyanate group included in a molecule
of the polyester prepolymer (A) is generally not less than 1,
preferably from 1.5 to 3, and more preferably from 1.8 to 2.5. When
the average number of the isocyanate group is too small, the
molecular weight of the resultant urea-modified polyester (which is
crosslinked and/or extended) decreases, thereby deteriorating the
hot offset resistance of the resultant toner.
The urea-modified polyester for use as a binder resin of the toner
for use in the present invention can be prepared by reacting a
polyester prepolymer (A) having an isocyanate group with an amine
(B).
Specific examples of the amines (B) include diamines (B1) ,
polyamines (B2) having three or more amino groups, amino alcohols
(B3) , amino mercaptans (B4) , amino acids (B5) and blocked amines
(B6) in which the amines (B1-B5) mentioned above are blocked. These
amines can be used alone or in combination.
Specific examples of the diamines (B1) include aromatic diamines
(e.g., phenylene diamine, diethyltoluene diamine and
4,4'-diaminodiphenyl methane); alicyclic diamines (e.g.,
4,4'-diamino-3,3'-dimethyldicyclohexyl methane, diaminocyclohexane
and isophoron diamine); aliphatic diamines (e.g., ethylene diamine,
tetramethylene diamine and hexamethylene diamine); etc.
Specific examples of the polyamines (B2) having three or more amino
groups include diethylene triamine, triethylene tetramine, etc.
Specific examples of the amino alcohols (B3) include ethanol amine,
hydroxyethyl aniline, etc. Specific examples of the amino mercaptan
(B4) include aminoethyl mercaptan, aminopropyl mercaptan, etc.
Specific examples of the amino acids (B5) include aminopropionic
acid, aminocaproic acid, etc. Specific examples of the blocked
amines (B6) include ketimine compounds which are prepared by
reacting one of the amines (B1-B5) mentioned above with a ketone
such as acetone, methyl ethyl ketone and methyl isobutyl ketone;
oxazoline compounds, etc. Among these amines, diamines (B1) and
mixtures of a diamine (B1) with a small amount of a polyamine (B2)
are preferably used.
The mixing ratio (i.e., the equivalence ratio [NCO]/[NHx]) of the
[NCO] group of the prepolymer (A) having an isocyanate group to the
[NHx] group of the amine (B) is from 1/2 to 2/1, preferably from
1/1.5 to 1.5/1 and more preferably from 1/1.2 to 1.2/1. When the
mixing ratio is too low or too high, the molecular weight of the
resultant urea-modified polyester decreases, resulting in
deterioration of the hot offset resistance of the resultant
toner.
The urea-modified polyesters for use in the toner can include a
urethane bond as well as a urea bond. The molar ratio of the urea
bond to the urethane bond is from 100/0 to 10/90, preferably from
80/20 to 20/80, and more preferably from 60/40 to 30/70. When the
molar ratio of the urea bond is too low, the hot offset resistance
of the resultant toner deteriorates.
The urea-modified polyesters can be prepared, for example, by a
method such as one-shot methods. Specifically, the polycondensation
reaction of a polyhydric alcohol with a polycarboxylic acid is
performed by heating the compounds to a temperature of from 150 to
280.degree. C. in the presence of an esterification catalyst such
as tetrabutoxytitanate and dibutyl tin oxide while removing
generated water (under a reduced pressure if necessary) to prepare
a polyester resin having a hydroxyl group. Then the polyester resin
is reacted with a polyisocyanate (PIC) at a temperature of from 40
to 140.degree. C. to prepare a polyester prepolymer (A) having an
isocyanate group. Further, the polyester prepolymer (A) is reacted
with an amine (B) at a temperature of from 0 to 140.degree. C. to
prepare a urea-modified polyester.
When a polyester prepolymer (A) is reacted with an amine (B),
solvents can be used if necessary. Specific examples of such
solvents include aromatic solvents such as toluene and xylene;
ketones such as acetone, methyl ethyl ketone and methyl isobutyl
ketone; esters such as ethyl acetate; amides such as
dimethylformamide and dimethylacetamide; ethers such as
tetrahydrofuran. In this regard, solvents inactive with the
isocyanate used are preferably used.
The molecular weight of the urea-modified polyesters can be
controlled using a reaction inhibitor, if desired. Specific
examples of such a reaction inhibitor include monoamines (e.g.,
diethyle amine, dibutyl amine, butyl amine and lauryl amine), and
blocked amines (i.e., ketimine compounds) prepared by blocking the
monoamines mentioned above.
The weight average molecular weight of the urea-modified polyester
for use in the toner is generally not less than 10,000, preferably
from 20,000 to 10,000,000 and more preferably from 30,000 to
1,000,000. When the weight average molecular weight is too low, the
hot offset resistance of the resultant toner deteriorates. The
number average molecular weight of the urea-modified polyester is
not particularly limited (i.e., the weight average molecular weight
of the urea-modified polyester is controlled so as to fall the
above-mentioned range) when an unmodified polyester resin is used
in combination therewith. When a urea-modified polyester is used
alone, the number average molecular weight thereof is from 2,000 to
15,000, preferably from 2,000 to 10,000 and more preferably from
2,000 to 8,000. When the molecular weight is too high, the low
temperature fixability of the resultant toner deteriorates and the
glossiness of color toner images decreases.
In the present invention, it is preferable to use a combination of
a urea-modified polyester with an unmodified polyester as the
binder resin of the toner. By using such a combination, the low
temperature fixability of the toner can be improved and in addition
the toner can produce color images having a high glossiness. In
this regard, polyester resins modified by a bond (such as urethane
bonding) other than a urea bond are considered as the unmodified
polyester in the present application.
When a combination of a urea-modified polyester with an unmodified
polyester resin is used as the binder resin, it is preferable that
the urea-modified polyester is at least partially mixed with the
unmodified polyester resin to improve the low temperature
fixability and hot offset resistance of the toner. Namely, it is
preferable that the urea-modified polyester has a molecular
structure similar to that of the unmodified polyester resin. The
mixing ratio (U/M) of an unmodified polyester (U) to a
urea-modified polyester (M) is from 20/80 to 95/5, preferably from
70/30 to 95/5, more preferably from 75/25 to 95/5, and even more
preferably from 80/20 to 93/7. When the added amount of the
modified polyester resin is too small, the hot offset resistance of
the toner deteriorates and in addition, it is impossible for the
toner to achieve a good combination of high temperature
preservability and low temperature fixability.
The binder resin including an unmodified polyester resin and a
urea-modified polyester resin preferably has a glass transition
temperature (Tg) of from 45 to 65.degree. C., and preferably from
45 to 60.degree. C. When the glass transition temperature is too
low, the heat resistance of the toner deteriorates. In contrast,
when the glass transition temperature is too high, the low
temperature fixability of the toner deteriorates.
Since a urea-modified polyester resin tends to be located on the
surface of toner particles, the toner has a relatively good high
temperature preservability compared with conventional toners
including a polyester even when the toner has a relatively low
glass transition temperature compared with the conventional
toners.
(Colorant)
The toner for use in the image forming apparatus of the present
invention includes a colorant. Suitable materials for use as the
colorant include known dyes and pigments.
Specific examples of the dyes and pigments include carbon black,
Nigrosine dyes, black iron oxide, NAPHTHOL YELLOW S, HANSA YELLOW
10G, HANSA YELLOW 5G, HANSA YELLOW G, Cadmium Yellow, yellow iron
oxide, loess, chrome yellow, Titan Yellow, polyazo yellow, Oil
Yellow, HANSA YELLOW GR, HANSA YELLOW A, HANSA YELLOW RN, HANSA
YELLOW R, PIGMENT YELLOW L, BENZIDINE YELLOW G, BENZIDINE YELLOW
GR, PERMANENT YELLOW NCG, VULCAN FAST YELLOW 5G, VULCAN FAST YELLOW
R, Tartrazine Lake, Quinoline Yellow LAKE, ANTHRAZANE YELLOW BGL,
isoindolinone yellow, red iron oxide, red lead, orange lead,
cadmium red, cadmium mercury red, antimony orange, Permanent Red
4R, Para Red, Fire Red, p-chloro-o-nitroaniline red, Lithol Fast
Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine BS, PERMANENT
RED F2R, PERMANENT RED F4R, PERMANENT RED FRL, PERMANENT RED FRLL,
PERMANENT RED F4RH, Fast Scarlet VD, VULCAN FAST RUBINE B,
Brilliant Scarlet G, LITHOL RUBINE GX, Permanent Red F5R, Brilliant
Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Toluidine Maroon,
PERMANENT BORDEAUX F2K, HELIO BORDEAUX BL, Bordeaux 10B, BON MAROON
LIGHT, BON MAROON MEDIUM, Eosin Lake, Rhodamine Lake B, Rhodamine
Lake Y, Alizarine Lake, Thioindigo Red B, Thioindigo Maroon, Oil
Red, Quinacridone Red, Pyrazolone Red, polyazo red, Chrome
Vermilion, Benzidine Orange, perynone orange, Oil Orange, cobalt
blue, cerulean blue, Alkali Blue Lake, Peacock Blue Lake, Victoria
Blue Lake, metal-free Phthalocyanine Blue, Phthalocyanine Blue,
Fast Sky Blue, INDANTHRENE BLUE RS, INDANTHRENE BLUE BC, Indigo,
ultramarine, Prussian blue, Anthraquinone Blue, Fast Violet B,
Methyl Violet Lake, cobalt violet, manganese violet, dioxane
violet, Anthraquinone Violet, Chrome Green, zinc green, chromium
oxide, viridian, emerald green, Pigment Green B, Naphthol Green B,
Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine
Green, Anthraquinone Green, titanium oxide, zinc oxide, lithopone
and the like. These materials are used alone or in combination.
The content of the colorant in the toner is preferably from 1 to
15% by weight, and more preferably from 3 to 10% by weight of the
toner.
Master batches, which are complexes of a colorant with a resin, can
be used as the colorant of the toner for use in the present
invention.
Specific examples of the resins for use as the binder resin of the
master batches include polymers of styrene or styrene derivatives,
copolymers of styrene or styrene derivatives with a vinyl monomer,
polymethyl methacrylate, polybutyl methacrylate, polyvinyl
chloride, polyvinyl acetate, polyethylene, polypropylene,
polyesters, epoxy resins, epoxy polyol resins, polyurethane resins,
polyamide resins, polyvinyl butyral resins, acrylic resins, rosin,
modified rosins, terpene resins, aliphatic or alicyclic hydrocarbon
resins, aromatic petroleum resins, chlorinated paraffin, paraffin
waxes, etc. These can be used alone or in combination.
(Charge Controlling Agent)
The toner for use in the image forming apparatus of the present
invention preferably includes a charge controlling agent. Any known
charge controlling agents can be used for the toner.
Suitable examples of the charge controlling agents include
Nigrosine dyes, triphenyl methane dyes, chromium-containing metal
complex dyes, molybdic acid chelate pigments, Rhodamine dyes,
alkoxyamines, quaternary ammonium salts, fluorine-modified
quaternary ammonium salts, alkylamides, phosphor and its compounds,
tungsten and its compounds, fluorine-containing activators, metal
salts of salicylic acid, metal salts of salicylic acid derivatives,
etc. Among these materials, metal salts of salicylic acid and
salicylic acid derivatives are preferably used. These materials can
be used alone or in combination.
Specific examples of the marketed charge controlling agents include
BONTRON.RTM. 03 (Nigrosine dye), BONTRON.RTM. P-51 (quaternary
ammonium salt), BONTRON.RTM. S-34 (metal-containing azo dye),
BONTRON.RTM. E-82 (metal complex of oxynaphthoic acid),
BONTRON.RTM. E-84 (metal complex of salicylic acid), and
BONTRON.RTM. E-89. (phenolic condensation product), which are
manufactured by Orient Chemical Industries Co., Ltd.; TP-302 and
TP-415 (molybdenum complex of quaternary ammonium salt), which are
manufactured by Hodogaya Chemical Co., Ltd.; COPY CHARGE.RTM. PSY
VP2038 (quaternary ammonium salt), COPY BLUE.RTM. (triphenyl
methane derivative), COPY CHARGE.RTM. NEG VP2036 and COPY
CHARGE.RTM. NX VP434 (quaternary ammonium salt), which are
manufactured by Hoechst AG; LRA-901, and LR-147 (boron complex),
which are manufactured by Japan Carlit Co., Ltd.; copper
phthalocyanine, perylene, quinacridone, azo pigments, and polymers
having a functional group such as a sulfonate group, a carboxyl
group, a quaternary ammonium group, etc.
Among these materials, materials capable of imparting a negative
polarity to the toner are preferably used.
The content of the charge controlling agent in the toner of the
present invention is determined depending on the variables such as
choice of binder resin, presence of additives, and dispersion
method. In general, the content of the charge controlling agent is
preferably from 0.1 to 10 parts by weight, and more preferably from
0.2 to 5 parts by weight, per 100 parts by weight of the binder
resin included in the toner. When the content is too high, the
charge quantity of the toner excessively increases, and thereby the
electrostatic attraction between the developing roller and the
toner increases, resulting in deterioration of fluidity and
decrease of image density.
(Release Agent)
The toner for use in the image forming apparatus of the present
invention can include a release agent. Suitable release agents
include waxes having a melting point of from 50 to 120.degree. C.
When such a wax is included in the toner, the wax is dispersed in
the binder resin and serves as a release agent while being present
at a location between a fixing roller and the toner particles in
the fixing process. Thereby the hot offset problem can be avoided
without applying an oil to the fixing roller used.
Specific examples of the release agent include natural waxes such
as vegetable waxes, e.g., carnauba wax, cotton wax, Japan wax and
rice wax; animal waxes, e.g., bees wax and lanolin; mineral waxes,
e.g., ozokelite and ceresine; and petroleum waxes, e.g., paraffin
waxes, microcrystalline waxes and petrolatum. In addition,
synthesized waxes can also be used. Specific examples of the
synthesized waxes include synthesized hydrocarbon waxes such as
Fischer-Tropsch waxes and polyethylene waxes; and synthesized waxes
such as ester waxes, ketone waxes and ether waxes. Further, fatty
acid amides such as 1,2-hydroxylstearic acid amide, stearic acid
amide and phthalic anhydride imide; and low molecular weight
crystalline polymers such as acrylic homopolymers and copolymers
having a long alkyl group in their side chain, e.g., poly-n-stearyl
methacrylate, poly-n-laurylmethacrylate and n-stearyl
acrylate-ethyl methacrylate copolymers, can also be used.
The above-mentioned charge controlling agent and release agent can
be kneaded with a master batch and a binder resin. Alternatively,
the charge controlling agent and the release agent can be added to
an organic solvent when the toner composition liquid is
prepared.
(External Additive)
A particulate inorganic material is typically mixed with toner
particles to assist in improving the fluidity, developing property
and charging ability of the toner particles. It is preferable for
such particulate inorganic materials to have a primary particle
diameter of from 5 nm to 2 .mu.m, and more preferably from 5 nm to
500 nm. In addition, it is preferable that the specific surface
area of such particulate inorganic materials measured by a BET
method is from 20 to 500 m.sup.2/g. The content of the external
additive is preferably from 0.01 to 5% by weight, and more
preferably from 0.01 to 2.0% by weight, based on the total weight
of the toner.
Specific examples of such particulate inorganic materials include
silica, alumina, titanium oxide, barium titanate, magnesium
titanate, calcium titanate, strontium titanate, zinc oxide, tin
oxide, quartz sand, clay, mica, sand-lime, diatom earth, chromium
oxide, cerium oxide, red iron oxide, antimony trioxide, magnesium
oxide, zirconium oxide, barium sulfate, barium carbonate, calcium
carbonate, silicon carbide, silicon nitride, etc.
Among these particulate inorganic materials, a combination of a
hydrophobic silica and a hydrophobic titanium oxide is preferably
used. In particular, when a combination of a hydrophobic silica
with a hydrophobic titanium oxide each having an average particle
diameter not greater than 50 nm is used as an external additive,
the electrostatic force and van der Waals' force between the
external additive and the toner particles can be improved, and
thereby the resultant toner has a proper charge quantity. In
addition, even when the toner is agitated in a developing device,
the external additive is hardly released from the toner particles,
and thereby image defects such as white spots and image omissions
are hardly produced. Further, the quantity of particles of the
toner remaining on image bearing members can be reduced.
Titanium oxide exhibits high stability to withstand environmental
conditions, and stably produce high density images. However,
titanium oxide has a drawback in that the charge rising property of
the toner deteriorates. Therefore it is not preferable that the
content of titanium oxide is higher than that of silica. When the
content of a hydrophobized titanium oxide is from 0.3 to 1.5% by
weight, the charge rising property of the resultant toner hardly
deteriorates. Therefore, images having good image qualities can be
stably produced even when images are repeatedly produced.
Next, the method for preparing the toner for use in the present
invention will be explained.
(1) Preparation of Toner Composition Liquid
At first, a toner composition liquid is prepared by dissolving or
dispersing toner components such as a colorant, an unmodified
polyester, a polyester prepolymer having an isocyanate group and a
release agent in an organic solvent. The organic solvent is
preferably a volatile solvent having a boiling point less than
100.degree. C. so as to be easily removed from the resultant toner
particles. Specific examples of such volatile solvents include
toluene, xylene, benzene, carbon tetrachloride, methylene chloride,
1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene,
chloroform, monochlorobenzene, dichloroethylidene, methyl acetate,
ethyl acetate, methyl ethyl ketone, and methyl isobutyl ketone.
These solvents can be used alone or in combination. In particular,
aromatic solvents such as toluene and xylene, and halogenated
hydrocarbons such as methylene chloride, 1,2-dichloroethane,
chloroform and carbon tetrachloride are preferably used.
The weight ratio of the solvent to the polyester prepolymer is
generally from 0/100 to 300/100, preferably from 0/100 to 100/100
and more preferably from 25/100 to 70/100.
(2) Emulsification of the Toner Composition Liquid
The toner composition liquid is then dispersed in an aqueous medium
in the presence of a surfactant and a particulate resin to prepare
an emulsion. Suitable materials for use as the aqueous medium
include water. In addition, organic solvents which can be mixed
with water can be added to water. Specific examples of such
solvents include alcohols such as methanol, isopropanol, and
ethylene glycol; dimethylformamide, tetrahydrofuran, cellosolves
such as methyl cellosolve, lower ketones such as acetone and methyl
ethyl ketone, etc.
The weight ratio of the aqueous medium to the toner composition
liquid is generally from 50/100 to 2,000/100 and preferably from
100/100 to 1,000/100. When the added amount of the aqueous medium
is too low, the toner composition liquid cannot be well dispersed,
and thereby toner particles having a desired particle diameter
cannot be prepared. Adding a large amount of aqueous medium is not
economical.
When the toner composition liquid is emulsified, a dispersant such
as surfactants and particulate resins are preferably included in
the aqueous medium.
Specific examples of the surfactants include anionic surfactants
such as alkylbenzene sulfonic acid salts, .alpha.-olefin sulfonic
acid salts, and phosphoric acid salts; cationic surfactants such as
amine salts (e.g., alkyl amine salts, aminoalcohol fatty acid
derivatives, polyamine fatty acid derivatives and imidazoline), and
quaternary ammonium salts (e.g., alkyltrimethyl ammonium salts,
dialkyldimethyl ammonium salts, alkyldimethyl benzyl ammonium
salts, pyridinium salts, alkyl isoquinolinium salts and
benzethonium chloride); nonionic surfactants such as fatty acid
amide derivatives, polyhydric alcohol derivatives; and ampholytic
surfactants such as alanine, dodecyldi(aminoethyl)glycin,
di)octylaminoethyle)glycin, and N-alkyl-N,N-dimethylammonium
betaine.
By using a fluorine-containing surfactant as the surfactant, good
effects can be produced even when the added amount is small.
Specific examples of anionic surfactants having a fluoroalkyl group
include fluoroalkyl carboxylic acids having from 2 to 10 carbon
atoms and their metal salts, disodium
perfluorooctanesulfonylglutamate, sodium
3-{omega-fluoroalkyl(C6-C11)oxy}-1-alkyl(C3-C4) sulfonate, sodium
3-{omega-fluoroalkanoyl(C6-C8)-N-ethylamino}-1-propanesulfonate,
fluoroalkyl(C11-C20) carboxylic acids and their metal salts,
perfluoroalkyl (C7-C13) carboxylic acids and their metal salts,
perfluoroalkyl(C4-C12)sulfonate and their metal salts,
perfluorooctanesulfonic acid diethanol amides,
N-propyl-N-(2-hydroxyethyl)perfluorooctanesulfone amide,
perfluoroalkyl(C6-C10)sulfoneamidepropyltrimethylammonium salts,
salts of perfluoroalkyl(C6-C10)-N-ethylsulfonyl glycin,
monoperfluoroalkyl(C6-C16)ethylphosphates, etc.
Specific examples of the marketed products of such surfactants
include SARFRON.RTM. S-111, S-112 and S-113, which are manufactured
by Asahi Glass Co., Ltd.; FLUORAD.RTM. FC-93, FC-95, FC-98 and
FC-129, which are manufactured by Sumitomo 3M Ltd.; UNIDYNE.RTM.
DS-101 and DS-102, which are manufactured by Daikin Industries,
Ltd.; MEGAFACE.RTM. F-10, F-120, F-113, F-191, F-812 and F-833
which are manufactured by Dainippon Ink and Chemicals, Inc.;
ECTOP.RTM. EF-102, 103, 104, 105, 112, 123A, 306A, 501, 201 and
204, which are manufactured by Tohchem Products Co., Ltd.;
FUTARGENT.RTM. F-100 and F150 manufactured by Neos; etc.
Specific examples of the cationic surfactants having a fluoroalkyl
group, which can disperse an oil phase including toner constituents
in water, include primary, secondary and tertiary aliphatic amines
having a fluoroalkyl group, aliphatic quaternary ammonium salts
such as perfluoroalkyl(C6-C10)sulfoneamidepropyltrimethylammonium
salts, benzalkonium salts, benzetonium chloride, pyridinium salts,
imidazolinium salts, etc. Specific examples of the marketed
products thereof include SARFRON.RTM. S-121 (from Asahi Glass Co.,
Ltd.); FLUORAD.RTM. FC-135 (from Sumitomo 3M Ltd.); UNIDYNE.RTM.
DS-202 (from Daikin Industries, Ltd.); MEGAFACE.RTM. F-150 and
F-824 (from Dainippon Ink and Chemicals, Inc.); ECTOP.RTM. EF-132
(from Tohchem Products Co., Ltd.); FUTARGENT.RTM. F-300 (from
Neos); etc.
Particulate resins are added to the aqueous medium to stabilize the
toner particles, which are prepared in the aqueous medium. It is
preferable that the added particulate resin covers the surface of
toner particles at a covering ratio of from 10 to 90%. Specific
examples of the particulate resins include particulate polymethyl
methacrylates (having a particle diameter of about 1 .mu.m or 3
.mu.m), particulate polystyrenes (having a particle diameter of
about 0.5 .mu.m or 2 .mu.m), and particulate styrene-acrylonitrile
copolymers (having a particle diameter of about 1 .mu.m). Specific
examples of the marketed products of the particulate resins include
PB-200H (from Kao Corp.), SGP (from Sohken Chemical &
Engineering Co., Ltd.), TECHNOPOLYMER SB (from Sekisui Plastics
Co., Ltd.), SGP-3G (from Sohken Chemical & Engineering Co.,
Ltd.), MICROPEARL (Sekisui Chemical Co., Ltd.), etc.
In addition, inorganic compounds can be used as a dispersant.
Specific examples of the inorganic compounds include tricalcium
phosphate, calcium carbonate, titanium oxide, colloidal silica, and
hydroxyapatite can be preferably used.
Further, it is preferable to stabilize the emulsion or dispersion
using a polymer protection colloid in combination with the
particulate resins and/or inorganic dispersants.
Specific examples of such protection colloids include polymers and
copolymers prepared using monomers such as acids (e.g., acrylic
acid, methacrylic acid, .alpha.-cyanoacrylic acid,
.alpha.-cyanomethacrylic acid, itaconic acid, crotonic acid,
fumaric acid, maleic acid and maleic anhydride), acrylic monomers
having a hydroxyl group (e.g., .beta.-hydroxyethyl acrylate,
.beta.-hydroxyethyl methacrylate, .beta.-hydroxypropyl acrylate,
.beta.-hydroxypropyl methacrylate, .gamma.-hydroxypropyl acrylate,
.gamma.-hydroxypropyl methacrylate, 3-chloro-2-hydroxypropyl
acrylate, 3-chloro-2-hydroxypropyl methacrylate,
diethyleneglycolmonoacrylic acid esters,
diethyleneglycolmonomethacrylic acid esters, glycerinmonoacrylic
acid esters, N-methylolacrylamide and N-methylolmethacrylamide),
vinyl alcohol and its ethers (e.g., vinyl methyl ether, vinyl ethyl
ether and vinyl propyl ether), esters of vinyl alcohol with a
compound having a carboxyl group (i.e., vinyl acetate, vinyl
propionate and vinyl butyrate); acrylic amides (e.g, acrylamide,
methacrylamide and diacetoneacrylamide) and their methylol
compounds, acid chlorides (e.g., acrylic acid chloride and
methacrylic acid chloride), and monomers having a nitrogen atom or
an alicyclic ring having a nitrogen atom (e.g., vinyl pyridine,
vinyl pyrrolidone, vinyl imidazole and ethylene imine).
In addition, polymers such as polyoxyethylene compounds (e.g.,
polyoxyethylene, polyoxypropylene, polyoxyethylenealkyl amines,
polyoxypropylenealkyl amines, polyoxyethylenealkyl amides,
polyoxypropylenealkyl amides, polyoxyethylene nonylphenyl ethers,
polyoxyethylene laurylphenyl ethers, polyoxyethylene stearylphenyl
esters, and polyoxyethylene nonylphenyl esters); and cellulose
compounds such as methyl cellulose, hydroxyethyl cellulose and
hydroxypropyl cellulose, can also be used as the polymeric
protective colloid.
Known dispersing machines can be used for emulsifying the toner
composition liquid in an aqueous medium. Suitable dispersing
machines include low speed shearing dispersion machines, high speed
shearing dispersion machines, friction dispersion machines, high
pressure jet dispersion machines, ultrasonic dispersion machines,
etc.
When high speed shearing dispersion machines are used, the rotation
number of the rotor is not particularly limited, but the rotation
number is generally from 1,000 to 30,000 rpm, and preferably from
5,000 to 20,000. The dispersion time is not particularly limited.
When a batch dispersion machines are used, the dispersion time is
generally from 0.1 to 5 minutes. The dispersion temperature is
preferably from 0 to 150.degree. C. and preferably from 40 to
98.degree. C.
(3) Reaction of Polyester Prepolymer (A) with Amine (B)
At the same time when preparing the emulsion, the polyester
prepolymer (A) having an isocyanate group is reacted with an amine
(B). The reaction is accompanied with crosslinking and/or polymer
chain growth of the prepolymer. The reaction time is determined
depending on the reactivity of the isocyanate group of the
polyester prepolymer with the amine used, and is generally from 10
minutes to 40 hours, and preferably from 2 to 24 hours. The
reaction temperature is generally from 0 to 150.degree. C., and
preferably from 40 to 98.degree. C.
In addition, known catalysts such as dibutyltin laurate and
tioctyltin layrate can be used for the reaction, if desired.
(4) Removal of Organic Solvent, and Washing and Drying
After the reaction, the organic solvent is removed from the
emulsion (i.e., the reaction product), followed by washing and
drying. Thus, toner particles having a spindle form are prepared.
In order to remove the organic solvent, the emulsion is gradually
heated while the emulsion is agitated so as to have a laminar flow.
In this case, it is preferable to remove the solvent in a certain
temperature range while strongly agitating the emulsion, so that
the resultant toner particles have a spindle form. When a
dispersant (such as calcium phosphate), which can be dissolved in
an acid or an alkali, is used, it is preferable to dissolve the
dispersant with hydrochloric acid to remove that from the toner
particles, followed by washing. In addition, it is possible to
remove such a dispersant by decomposing the dispersant using an
enzyme.
(5) Addition of External Additive
Next, a charge controlling agent is fixed on the thus prepared
toner particles and an external additive such as particulate
inorganic materials (e.g., silica and titanium oxide) is added
thereto. If desired, a particulate lubricant can also be added
thereto. These materials can be added by a method using a known
mixer or the like.
By using such a method, a toner having a small particle diameter
and a sharp particle diameter distribution can be easily prepared.
By controlling the agitation during the solvent removing operation,
the particle form of the toner can be easily changed from spherical
forms to rugby-ball forms. In addition, the surface conditions of
the toner particles can be controlled, specifically, the surface
can be freely changed from smooth surface to rough surface like
pickled plum.
Next, drive controlling of the toner pump 60 and the sub-hopper 68
will be explained.
FIG. 10 is a block diagram for explaining drive controlling of the
toner pump 60 and the sub-hopper 68.
As illustrated in FIG. 10, the controller 600 controls an image
forming section 151 including the optical writing unit 21, the
photoreceptor 1, a charger, the developing device 4, a drum
cleaner, and a discharger, according to the image information
obtained by the scanner 300 to perform image forming operations.
The controller 600 activates the sub-hopper drive clutch 68a to
drive the sub-hopper 68 after every image forming operation of the
image forming section 151. In this regard, the controller 600
controls the sub-hopper drive clutch 68a such that the greater
image area proportion the recorded image has, the longer the ON
time of the sub-hopper drive clutch 68a. By performing such a
controlling operation, the volume of the developer present in the
developing device can be controlled to fall in a predetermined
range.
The controller 600 performs toner detection at a predetermined
interval (2 seconds in this example) using the toner sensor 610.
When the toner sensor 610 determines that the amount of toner at
the position of the toner sensor is less than a predetermined
amount, the controller 600 activates the pump drive clutch 60a,
thereby driving the toner pump 60 to supply the premix toner to the
sub-hopper 68. In this case, the pump drive clutch 60a is turned
off at the next toner detection time (i.e., 2 seconds after the
last toner detection) while the toner sensor 610 determines whether
or not the amount of toner is less than the predetermined amount.
When the toner sensor 610 determines that the amount of toner is
still less than the predetermined amount, the controller 600
activates the pump drive clutch 60a to drive the pump 60. This
controlling such that the pump drive clutch 60a is activated for a
predetermined time, followed by inactivating is repeated until the
amount of toner becomes not less than the predetermined amount.
In contrast, when the toner sensor 610 determines that the amount
of toner at the position of the toner sensor is not less than the
predetermined amount, the toner detection operation is performed at
regular intervals (i.e., 2 seconds) while turning off the pump
drive clutch 60a.
When the toner sensor 610 continues to determine that the amount of
toner is less than the predetermined amount even after the
controlling that the pump drive clutch 60a is activated for a
predetermined time, followed by inactivating is repeated, the
controller 600 determines that the toner bottle 120 is in the
near-empty state.
Specifically, the copier 100 determines the amount of the toner
remaining in the toner bottle 120 by measuring a property
influenced by the amount of toner supplied by the toner pump 60. In
this example, the property is the amount of the toner present in
the sub-hopper 68. Namely, if the toner sensor 610 does not
determine that the amount of toner is not less than the
predetermined amount even after the controlling that the pump drive
clutch 60a is activated and then inactivated is repeated, the
controller 600 determines that the toner bottle 120 is in the
near-empty state. Thus, the toner sensor 610 and the controller 600
constitute the residual toner detector.
When it is determined that the toner bottle 120 is in the
near-empty state, a near-empty message is displayed in a display
620 to notify the user that the premix toner is exhausted.
In this example, if the toner sensor 610 continues to determine
that the amount of toner is less than the predetermined amount even
after the controlling that the pump drive clutch 60a is activated
and then inactivated is repeated ten times, the controller 600
determines that the toner bottle 120 is in the near-empty state
(i.e., the premix toner is exhausted).
When the near-empty message is displayed in the display 620, the
user replaces the toner bottle 120 with a new toner bottle. When
the new toner bottle is set, the controller 600 turns on the pump
drive clutch 60a to drive the toner pump 60, thereby supplying the
premix toner in the new toner bottle 120 to the sub-hopper 68. When
the toner sensor 610 determines that the amount of toner in the
sub-hopper 68 is not less than the predetermined amount, the toner
bottle replacing operation is completed and the pump drive clutch
60a is inactivated.
Next, the drive controlling of the screw pump in an image forming
apparatus having a background screw pump will be explained.
FIG. 11 is a timing chart for explaining drive controlling of a
screw pump in a background image forming apparatus. As illustrated
in FIG. 11, even after the controller decides that the toner is
ended, the background image forming apparatus continues to perform
image forming operations until the predetermined conditions (such
as printing of a predetermined amount of copies and elapse of a
predetermined time) are satisfied. In addition, the screw pump in
the background image forming apparatus continues to perform the
normal driving operation until the image forming operation is
stopped.
In this regard, the normal driving operation of the screw pump
means the operation of the screw pump performed when a sufficient
amount of premix toner is contained in the toner container. In the
normal driving operation of the image forming apparatus of the
present invention, the screw pump is activated for a predetermined
time (2 seconds), and then inactivated for a predetermined time
(0.2 seconds) while the toner detection operation is performed. In
this regard, when it is determined that a predetermined amount of
toner is not present, the screw pump is activated again for the
predetermined time (2 seconds). In general, when a toner end
decision is made, the detection result such that the sufficient
amount of toner is not present is continuously produced. Therefore,
in background image forming apparatus, activation and inactivation
of the toner pump are repeatedly performed around the toner end
decision, i.e., the toner pump is intermittently activated.
In general image forming apparatus, even after the toner supply by
the screw pump is stopped, the toner (or premix toner) is present
in the sub-hopper. Therefore, by supplying the toner in the
sub-hopper to the developing device, the amount of the developer in
the developing device and the concentration of toner in the
developer can be maintained and thereby the image forming
operations can be performed.
When the amount of the toner contained in the toner bottle becomes
less than a certain amount, the amount of the toner fed by the
screw pump varies. Therefore, even when the screw pump is driven,
the amount of toner in the sub-hopper cannot be increased to the
predetermined amount and the toner end decision is made. Thus, when
the toner end decision is made, a small amount of toner remains in
the toner bottle. Therefore, in conventional image forming
apparatus, the normal operation of the screw pump is performed even
after the toner end decision is made, to reduce the amount of the
toner contained in the toner bottle.
Screw pumps generate a suction force while the rotor rubs the
stator, thereby generating frictional heat in the pumps. When a
sufficient amount of toner is present in the toner bottle, a
certain amount of toner enters into the screw pump through the
suction opening and then discharged from the discharge opening. In
this case, the frictional heat is transferred to the toner fed
through the screw pump and is then discharged from the pump
together with the toner, thereby preventing increase of the
internal temperature of the screw pump. However, when the amount of
toner remaining in the toner bottle is small, the amount of toner
entering into the pump decreases even when the screw pump is
operated normally. Therefore, the quantity of frictional heat
discharged from the pump together with the toner decreases. In this
case, when the toner pump is normally operated, the internal
temperature of the screw pump increases.
When controlling such that even when a toner end decision is made,
the screw pump is driven to operate is performed, the toner end
decision is continuously made when the amount of toner in the toner
bottle is small. When a sufficient amount of toner is present in
the toner bottle, the toner sensor makes a decision such that the
toner is present in a predetermined amount after the screw pump is
operated. In this case, the screw pump is stopped, and thereby the
screw pump is cooled. In contrast, when a sufficient amount of
toner is not present in the toner bottle, the toner end decision is
continuously made and therefore the screw pump is operated without
pause, resulting in increase of the internal temperature of the
screw pump.
In this case, when a low temperature fixable toner is used for the
image forming apparatus, the toner heated at a high temperature in
the screw pump aggregates after being cooled. Thereby, the stator
is further abraded by the aggregated toner, resulting in
deterioration of suction power of the screw pump. Although low
temperature fixable toner can be fixed at a relatively low fixing
temperature, such toner is typically inferior to conventional
toners in heat resistance and therefore the toner deteriorates at a
relatively low temperature.
In the copier 100 of the present invention, when a toner end
decision is made, the degree of increase of the internal
temperature of the screw pump is reduced by reducing the operation
time of the toner pump 60, stopping the operation of the toner
pump, or decreasing the revolution of the toner pump. By using this
method, the problem in that the suction power of the toner pump
deteriorates can be avoided.
Having generally described this invention, further understanding
can be obtained by reference to certain specific examples which are
provided herein for the purpose of illustration only and are not
intended to be limiting.
EXAMPLES
Example 1
One method for controlling increase of the internal temperature of
a screw pump will be explained by reference to drawing.
FIG. 12 is a timing chart for explaining drive controlling of the
toner pump 60 of the toner supplying device 500 of the copier 100
in this example.
In this example, when the controller 600 judges that the toner
bottle 120 achieves a near-empty state (hereinafter sometimes
referred to as a toner end decision) on the basis of the signal
sent from the toner sensor 610 provided on the sub-hopper 68, the
copier notifies the user by displaying a toner end message. After
the toner end decision is made, the copier 100 continues the image
forming operations for a while using the toner remaining in the
sub-hopper 68. In this example, the copier produces 400 images
after the toner end decision is made, and then stops the image
forming operation. As illustrated in FIG. 12, after the toner end
decision, the operation of the toner pump 60 is stopped. Namely,
the toner pump 60 is stopped before the copier 100 is stopped.
The time when the operation of the toner pump 60 is stopped is
determined depending on the properties (typically, heat resistance)
of the toner used. If the toner has low heat resistance, it is
preferable to stop the toner pump soon after the toner end
decision. In this example, as illustrated in FIG. 12, the toner
pump is stopped soon after the toner end decision.
By stopping the toner pump soon after the toner end decision, the
degree of increase in the internal temperature of the toner pump 60
can be reduced. Thereby, melting of the toner in the toner pump 60
can be prevented, resulting in prevention of the problem in that
the suction power of the toner pump is deteriorated due to abrasion
of the stator 69 caused by the toner aggregated in the pump.
When a toner, which is not a low temperature fixable toner and has
relatively good heat resistance, is used, the toner pump is
preferably operated as long as possible to reduce the amount of
toner remaining in the toner bottle.
Example 2
Another method for controlling increase of the internal temperature
of a screw pump will be explained by reference to drawing.
FIG. 13 is another timing chart for explaining drive controlling of
the toner pump 60 of the toner supplying device 500 of the copier
100 in this example.
In this example, when the controller 600 makes a toner end decision
on the basis of the signal sent from the toner sensor 610 provided
on the sub-hopper 68, the copier notifies the user by displaying a
toner end message. After the toner end decision is made, the copier
100 continues the image forming operations for a while using the
toner remaining in the sub-hopper 68. In this example, the copier
produces 400 images after the toner end decision is made, and then
stops the image forming operation.
As illustrated in FIG. 13, after the toner end decision, the number
of driving of the toner pump per unit time is controlled to fall in
a predetermined range. In this example, the toner pump 60 is
operated not more than once per 10 seconds as illustrated in FIG.
13. Specifically, in this example, the toner pump 60 is operated
for 2 seconds and then stopped for 8 seconds. Thus, the toner pump
60 is operated under a restricted condition. After the toner pump
60 is operated for a while under a restricted condition, the toner
pump 60 is stopped before or at the same time the copier is
stopped.
In this example, the ratio (S/D) of the stopping period (S) of the
toner pump 60 to the driving period (D) thereof is relatively
increased after the toner end decision compared to the ration (S/D)
in the normal operation of the toner pump 60 performed before the
toner end decision. By using this method, occurrence of the problem
in that the internal temperature of the toner pump 60 increases,
resulting in aggregation of the toner therein, thereby seriously
abrading the stator 69 can be prevented.
The restricted condition for the operation of the toner pump is
determined depending on the properties (typically, heat resistance)
of the toner used.
Example 3
Another method for controlling increase of the internal temperature
of a screw pump will be explained by reference to drawing.
FIG. 14 is another timing chart for explaining drive controlling of
the toner pump 60 of the toner supplying device 500 of the copier
100 in this example.
In this example, when the controller 600 makes a toner end decision
on the basis of the signal sent from the toner sensor 610 provided
on the sub-hopper 68, the copier notifies the user by displaying a
toner end message. After the toner end decision is made, the copier
100 continues the image forming operations for a while using the
toner remaining in the sub-hopper 68. In this example, the copier
produces 400 images after the toner end decision is made, and then
stops the image forming operation.
As illustrated in FIG. 14, after the toner end decision, the number
of revolution of the toner pump 60 is decreased, for example, by
decreasing the number of revolution of the driving motor 66 serving
as a driving source of the toner pump 60. After the toner pump 60
is operated under such a restricted condition for a while, the
toner pump 60 is stopped before or at the same time the copier is
stopped.
In the toner supplying device 500, the toner pump 60 is rotated at
a revolution of from 200 to 400 rpm in the normal driving period
(i.e., in the pump driving period in FIG. 14). After the toner end
decision is made, the toner pump 60 is rotated at a relatively low
revolution of from 100 to 200 rpm. In this regard, the revolution
of the pump after the toner end decision is determined depending on
the properties (preferably heat resistance) of the toner used.
By using this method, occurrence of the problem in that the
internal temperature of the toner pump 60 increases due to friction
between the rotor and stator, resulting in aggregation of the toner
therein, thereby seriously abrading the stator 69 can be
prevented.
Thus, the image forming apparatus of the present invention may be
an image forming apparatus including an image bearing member
configured to bear an electrostatic image thereon; a developing
device, which has a developer containing portion containing a
developer including at least a toner and which is configured to
develop the electrostatic image with the developer to form a toner
image on the image bearing member; and a toner supplying device
configured to supply a developer supplement including at least the
toner to the developer containing portion, and including: a toner
container containing the developer supplement; a feeding passage
configured to connect the toner container with the developer
containing portion; a pump, in which a first member is moved while
rubbing a second member to feed the developer supplement from the
toner container to the developer containing portion through the
feeding passage; and a residual toner detector configured to detect
an amount of the developer supplement remaining in the toner
container to determine whether the toner container is in a
near-empty state, wherein even after the residual toner detector
determines that the toner container is in a near-empty state, the
image forming apparatus continues the image forming operations as
long as a predetermined condition is satisfied while decreasing the
driving speed of the pump (i.e., decreasing the moving speed of the
first member of the pump).
Example 4
Another method for controlling increase of the internal temperature
of a screw pump will be explained by reference to drawing.
FIG. 15 is another timing chart for explaining drive controlling of
the toner pump 60 of the toner supplying device 500 of the copier
100 in this example.
In this example, when the controller 600 makes a toner end decision
on the basis of the signal sent from the toner sensor 610 provided
on the sub-hopper 68, the copier notifies the user by displaying a
toner end message. After the toner end decision is made, the copier
100 continues the image forming operations for a while using the
toner remaining in the sub-hopper 68. In this example, the copier
produces 400 images after the toner end decision is made, and then
stops the image forming operation.
As illustrated in FIG. 15, after the toner end decision, the
periods of one driving operation and one stopping operation of the
toner pump 60 are prolonged. Specifically, in this example, the
period of one driving operation is 10 seconds after the toner end
decision whereas the period is 2 seconds before the toner end
decision (i.e., in the normal driving operation). By prolonging the
period of one driving operation, the number of drive starting and
stopping operations per a unit time can be decreased. In this
regard, at the start of driving, the suction power of the toner
pump 60 is not so strong but the rotor 61 rubs the stator 69.
Therefore, the stator 69 is easily abraded and frictional heat is
easily generated. By using the above-mentioned method, the time
period during which frictional heat is generated by the rotor and
stator can be reduced.
In addition, in this example, the period of one stopping operation
following one driving operation is 20 seconds after the toner end
decision whereas the period is 0.2 seconds before the toner end
decision (i.e., in the normal driving operation). By prolonging the
pump stopping period, the toner pump 60 can be well cooled.
As mentioned above, since the time period during which frictional
heat is generated by the rotor and stator is shortened while the
time period during which the toner pump is cooled is prolonged,
occurrence of the problem in that the internal temperature of the
toner pump increases can be prevented. By using this method,
occurrence of the problem in that the internal temperature of the
toner pump 60 increases due to friction between the rotor and
stator, resulting in aggregation of the toner therein, thereby
seriously abrading the stator 69 can be prevented.
In addition, the stator 69 is easily abraded at the beginning and
end of the driving operations. In this example (Example 4), the
number of the driving and stopping operations is reduced by
prolonging the pump driving period of the mohno pump to reduce the
degree of abrasion of the stator 69.
The prolonged pump driving period and pump stopping period are
determined depending on the properties (preferably, heat
resistance) of the toner used.
As mentioned above, the toner bottle 120 preferably contains
premixed toner including a carrier and a toner. The purpose of
using a premix toner is to prolong the life of the developer in the
developing device 4. Specifically, by supplying a premix toner to
the developing device 4, the carrier in the developer in the
developing device is replaced little by little with a fresh carrier
included in the supplied premix toner. Therefore, the developer in
the developing device can maintain good developing property,
thereby producing high quality images for a long period of
time.
However, since the main component of the carrier is iron (Fe), it
is possible that abrasion of the stator 69 made of a rubber is
accelerated by the carrier, resulting in deterioration of the
suction power of the toner pump 60. Although the copier 100 uses a
premix toner, the copier hardly causes such a stator abrasion
problem because of controlling increase of the internal temperature
of the toner pump 60 after a toner end decision.
In the above explanation, the toner supplying device 500 directly
sucks the premix toner in the toner bottle 120 by a negative
pressure formed by the toner pump 60. However, the toner supplying
device is not limited thereto. For example, it is possible to use a
toner supplying device including a toner receiving portion, which
is located on an uppermost stream portion in the toner supplying
device and receives the toner (or premix toner) from a toner
bottle, wherein the toner in the toner receiving portion is sucked
through a toner feeding passage by forming a negative pressure
using a screw pump. In addition, the toner pump 60 is not limited
to a screw pump, and any devices in which one of at least two
members is moved while rubbing the other member to form a negative
pressure at a suction opening can be used. Specific examples of
such devices include Roots-type blowers, rotary compressors, vane
compressors, etc.
As mentioned above, the copier 100 serving as an image forming
apparatus includes the developing device 4 which develops an
electrostatic latent image formed on the photoreceptor 1 serving as
a latent image bearing member using the developer included in the
developing device; and the toner supplying device 500 configured to
supply the toner (preferably, premix toner) to the developer
containing portion of the developing device 4. The toner supplying
device 500 includes the toner bottle 120 serving as a toner
container, and the toner supplying tube 65, which serves as a toner
feeding passage and which connects the toner bottle 120 with the
developer containing portion. The toner supplying device 500
further includes the toner pump 60 serving as a pumping device in
which one (rotor 61) of at least two members moves while rubbing
the other member (stator 69) to form a negative pressure at the
toner suction opening 63, thereby feeding the toner through the
toner supplying tube 65 due to airflow in the toner supplying
tube.
In addition, the copier 100 further includes the toner sensor 610
serving as a residual toner detector configured to detect the
amount of residual toner in the toner bottle 120 by detecting a
property influenced by the amount of the toner fed by the toner
pump 60, and the controller 600 configured to control the
operations of the copier. In the copier 100, the property
influenced by the amount of the toner fed by the toner pump 60 is
the amount of the toner in the sub-hopper 68. Even after the
controller 600 makes a toner end decision such that the toner in
the toner bottle is in a near-empty state, the controller permits
the copier to produce a predetermined number of images (for
example, 400 images). This is one example of the above-mentioned
predetermined condition to be satisfied.
In Example 1, after the toner end decision, the toner pump 60 is
stopped to prevent the internal temperature of the toner pump from
increasing due to decrease of the toner fed through the toner pump.
Therefore, occurrence of the problem in that the toner in the toner
pump is melted and aggregated, thereby abrading the stator 69,
resulting in decrease of the suction power of the toner pump can be
prevented.
In Example 2, after the toner end decision, driving of the toner
pump is controlled such that the ratio (S/D) of the stopping period
(S) to the driving period (D) is greater than that before the
residual toner detector makes the near-empty detection. By using
this method, the time period during which the toner pump is heated
by the frictional heat caused by the friction between the rotor and
stator can be reduced. Therefore, increase of the internal
temperature of the toner pump due to decrease of the toner fed
through the toner pump can be controlled, and occurrence of the
problem in that the toner in the toner pump is melted and
aggregated, thereby abrading the stator 69, resulting in decrease
of the suction power of the toner pump can be prevented.
In Example 3, after the toner end decision, the revolution of the
rotor 61 of the toner pump 60 is relatively decreased compared to
that in the normal toner supplying operation. By using this method,
the quantity of frictional heat caused by the toner pump 60 per
unit time can be reduced. Therefore, increase of the internal
temperature of the toner pump due to decrease of the toner fed
through the toner pump can be controlled, and occurrence of the
problem in that the toner in the toner pump is melted and
aggregated, thereby abrading the stator 69, resulting in decrease
of the suction power of the toner pump can be prevented.
In Example 4, after the toner end decision, each of the pump
driving period and the pump stopping period is relatively prolonged
compared to those in the normal toner supplying operation. By using
this method, the frequency of repetition of pump driving and
stopping can be reduced, and thereby the quantity of frictional
heat caused by the toner pump 60 per unit time can be reduced. In
addition, since the pump stopping period is prolonged, the toner
pump can be well cooled. Therefore, increase of the internal
temperature of the toner pump due to decrease of the toner fed
through the toner pump can be controlled, and occurrence of the
problem in that the toner in the toner pump is melted and
aggregated, thereby abrading the stator 69, resulting in decrease
of the suction power of the toner pump can be prevented.
In addition, the toner pump 60 of the toner supplying device 500 is
a screw pump including the stator 69 made of an elastic material
and having a spiral groove on the cylindrical inner surface thereof
and the rotor 61 which is made of a metal and which rotates in the
stator while rubbing the inner surface of the stator to feed the
toner in the axial direction thereof. By using a screw pump for the
toner pump 60, space can be saved.
The toner contained in the toner bottle 120 is preferably a toner
prepared by a method including dissolving or dispersing toner
components including at least a polyester prepolymer including a
functional group having a nitrogen atom, a polyester, a colorant,
and a release agent in an organic solvent to prepare a toner
composition liquid, and subjecting the toner composition liquid to
a crosslinking reaction and/or a polymer chain growth reaction in
an aqueous medium. The toner has good low temperature fixability.
By using the toner, the fixing temperature can be decreased,
resulting in energy saving of the copier 100.
The toner contained in the toner bottle 120 is preferably a premix
toner including a carrier and a toner, wherein the concentration of
the toner is higher than that in the developer contained in the
developing device 4. In this case, the carrier in the developer in
the developing device 4 can be replaced with a fresh carrier little
by little. Therefore, the developer in the developing device 4 can
maintain good developing property, resulting in formation of high
quality images for a long period of time.
This document claims priority and contains subject matter related
to Japanese Patent Application No. 2007-239822, filed on Sep. 14,
2007, incorporated herein by reference.
Having now fully described the invention, it will be apparent to
one of ordinary skill in the art that many changes and
modifications can be made thereto without departing from the spirit
and scope of the invention as set forth therein.
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